diff --git a/toolchain/check/handle_impl.cpp b/toolchain/check/handle_impl.cpp
index d80b0ad424843..e2ac36c33e0cd 100644
--- a/toolchain/check/handle_impl.cpp
+++ b/toolchain/check/handle_impl.cpp
@@ -104,7 +104,6 @@ auto HandleParseNode(Context& context, Parse::DefaultSelfImplAsId node_id)
                       "`impl as` can only be used in a class");
     context.emitter().Emit(node_id, ImplAsOutsideClass);
     self_type_id = SemIR::ErrorInst::SingletonTypeId;
-    return false;
   }
 
   // Build the implicit access to the enclosing `Self`.
@@ -146,14 +145,14 @@ static auto ExtendImpl(Context& context, Parse::NodeId extend_node,
     DiagnoseExtendImplOutsideClass(context, node_id);
     return false;
   }
-  auto& parent_scope = context.name_scopes().Get(parent_scope_id);
-
   // TODO: This is also valid in a mixin.
   if (!TryAsClassScope(context, parent_scope_id)) {
     DiagnoseExtendImplOutsideClass(context, node_id);
     return false;
   }
 
+  auto& parent_scope = context.name_scopes().Get(parent_scope_id);
+
   if (params_node.has_value()) {
     CARBON_DIAGNOSTIC(ExtendImplForall, Error,
                       "cannot `extend` a parameterized `impl`");
@@ -387,7 +386,8 @@ static auto BuildImplDecl(Context& context, Parse::AnyImplDeclId node_id,
   context.ReplaceInstBeforeConstantUse(impl_decl_id, impl_decl);
 
   // For an `extend impl` declaration, mark the impl as extending this `impl`.
-  if (introducer.modifier_set.HasAnyOf(KeywordModifierSet::Extend)) {
+  if (self_type_id != SemIR::ErrorInst::SingletonTypeId &&
+      introducer.modifier_set.HasAnyOf(KeywordModifierSet::Extend)) {
     auto extend_node = introducer.modifier_node_id(ModifierOrder::Decl);
     if (impl_info.generic_id.has_value()) {
       SemIR::TypeId type_id = context.insts().Get(constraint_inst_id).type_id();
diff --git a/toolchain/check/impl.cpp b/toolchain/check/impl.cpp
index 3a5b37a58ad9a..5931591edd884 100644
--- a/toolchain/check/impl.cpp
+++ b/toolchain/check/impl.cpp
@@ -84,6 +84,10 @@ auto ImplWitnessForDeclaration(Context& context, const SemIR::Impl& impl)
     -> SemIR::InstId {
   CARBON_CHECK(!impl.has_definition_started());
 
+  if (impl.self_id == SemIR::ErrorInst::SingletonInstId) {
+    // When 'impl as' is invalid, the self type is an error.
+    return SemIR::ErrorInst::SingletonInstId;
+  }
   auto facet_type_id = context.GetTypeIdForTypeInst(impl.constraint_id);
   if (facet_type_id == SemIR::ErrorInst::SingletonTypeId) {
     return SemIR::ErrorInst::SingletonInstId;
diff --git a/toolchain/check/impl_lookup.cpp b/toolchain/check/impl_lookup.cpp
index 77a906c5a037b..cef737797e855 100644
--- a/toolchain/check/impl_lookup.cpp
+++ b/toolchain/check/impl_lookup.cpp
@@ -145,14 +145,11 @@ auto LookupImplWitness(Context& context, SemIR::LocId loc_id,
     // constraint, the unique `interface` declaration.)
 
     auto specific_id = SemIR::SpecificId::None;
-    // This check comes first to avoid deduction when the witness_id is missing.
-    // We use an error value to indicate an error during creation of the impl,
-    // such as a recursive impl which will cause deduction to recurse
-    // infinitely.
-    if (!impl.witness_id.has_value() ||
-        impl.witness_id == SemIR::ErrorInst::SingletonInstId) {
-      // TODO: Diagnose if the impl isn't defined yet?
-      return SemIR::InstId::None;
+    // This check comes first to avoid deduction with an invalid impl. We use an
+    // error value to indicate an error during creation of the impl, such as a
+    // recursive impl which will cause deduction to recurse infinitely.
+    if (impl.witness_id == SemIR::ErrorInst::SingletonInstId) {
+      continue;
     }
     if (impl.generic_id.has_value()) {
       specific_id = DeduceImplArguments(context, loc_id, impl, type_const_id,
@@ -175,6 +172,10 @@ auto LookupImplWitness(Context& context, SemIR::LocId loc_id,
       // the constraint's interfaces.
       continue;
     }
+    if (!impl.witness_id.has_value()) {
+      // TODO: Diagnose if the impl isn't defined yet?
+      return SemIR::InstId::None;
+    }
     LoadImportRef(context, impl.witness_id);
     if (specific_id.has_value()) {
       // We need a definition of the specific `impl` so we can access its
diff --git a/toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon b/toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon
index 4e5b0c02ed169..b589a7fb46229 100644
--- a/toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon
+++ b/toolchain/check/testdata/function/declaration/no_prelude/name_poisoning.carbon
@@ -311,10 +311,21 @@ interface A {
 class X {
   extend impl as A {
     fn F() { return; }
-    // CHECK:STDERR: fail_using_poisoned_name_in_impl_outside_class.carbon:[[@LINE+4]]:10: error: `impl as` can only be used in a class [ImplAsOutsideClass]
+    // CHECK:STDERR: fail_using_poisoned_name_in_impl_outside_class.carbon:[[@LINE+15]]:10: error: `impl as` can only be used in a class [ImplAsOutsideClass]
     // CHECK:STDERR:     impl as B {}
     // CHECK:STDERR:          ^~
     // CHECK:STDERR:
+    // CHECK:STDERR: fail_using_poisoned_name_in_impl_outside_class.carbon:[[@LINE+11]]:13: error: `Core.ImplicitAs` implicitly referenced here, but package `Core` not found [CoreNotFound]
+    // CHECK:STDERR:     impl as B {}
+    // CHECK:STDERR:             ^
+    // CHECK:STDERR:
+    // CHECK:STDERR: fail_using_poisoned_name_in_impl_outside_class.carbon:[[@LINE-10]]:3: error: missing implementation of B in impl of interface A [ImplMissingFunction]
+    // CHECK:STDERR:   extend impl as A {
+    // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
+    // CHECK:STDERR: fail_using_poisoned_name_in_impl_outside_class.carbon:[[@LINE-16]]:3: note: associated function B declared here [AssociatedFunctionHere]
+    // CHECK:STDERR:   fn B();
+    // CHECK:STDERR:   ^~~~~~~
+    // CHECK:STDERR:
     impl as B {}
   }
 }
@@ -1189,9 +1200,21 @@ fn F() {
 // CHECK:STDOUT:   %A.assoc_type: type = assoc_entity_type %A.type [template]
 // CHECK:STDOUT:   %assoc0: %A.assoc_type = assoc_entity element0, @A.%B.decl [template]
 // CHECK:STDOUT:   %X: type = class_type @X [template]
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (<error>) [template]
+// CHECK:STDOUT:   %F.type: type = fn_type @F [template]
+// CHECK:STDOUT:   %F: %F.type = struct_value () [template]
+// CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [template]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .A = %A.decl
+// CHECK:STDOUT:     .X = %X.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %A.decl: type = interface_decl @A [template = constants.%A.type] {} {}
+// CHECK:STDOUT:   %X.decl: type = class_decl @X [template = constants.%X] {} {}
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: interface @A {
 // CHECK:STDOUT:   %Self: %A.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
@@ -1204,21 +1227,46 @@ fn F() {
 // CHECK:STDOUT:   witness = (%B.decl)
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: impl @impl: <unexpected>.inst26.loc8_15 as <unexpected>.inst27.loc8_18;
+// CHECK:STDOUT: impl @impl.1: %Self.ref as %A.ref {
+// CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {} {}
+// CHECK:STDOUT:   %.loc25: type = converted @impl.2.%B.ref, <error> [template = <error>]
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, <error> [template = <error>]
+// CHECK:STDOUT:     %B.ref: %A.assoc_type = name_ref B, @A.%assoc0 [template = constants.%assoc0]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   witness = @X.%impl_witness
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.2: %Self.ref as <error> {
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   witness = <error>
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: class @X {
-// CHECK:STDOUT:   complete_type_witness = invalid
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%X [template = constants.%X]
+// CHECK:STDOUT:     %A.ref: type = name_ref A, file.%A.decl [template = constants.%A.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (<error>) [template = constants.%impl_witness]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
+// CHECK:STDOUT:   complete_type_witness = %complete_type
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
 // CHECK:STDOUT:   .Self = constants.%X
-// CHECK:STDOUT:   extend <unexpected>.inst27.loc8_18
+// CHECK:STDOUT:   extend @impl.1.%A.ref
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: generic fn @B(@A.%Self: %A.type) {
 // CHECK:STDOUT:   fn();
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: fn @F();
+// CHECK:STDOUT: fn @F() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: specific @B(constants.%Self) {}
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/impl/fail_impl_as_scope.carbon b/toolchain/check/testdata/impl/fail_impl_as_scope.carbon
index c930a7d038afa..1067c0c18c134 100644
--- a/toolchain/check/testdata/impl/fail_impl_as_scope.carbon
+++ b/toolchain/check/testdata/impl/fail_impl_as_scope.carbon
@@ -47,17 +47,39 @@ fn Function() {
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %Simple.type: type = facet_type <@Simple> [template]
 // CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic]
-// CHECK:STDOUT:   %F.type: type = fn_type @F [template]
-// CHECK:STDOUT:   %F: %F.type = struct_value () [template]
+// CHECK:STDOUT:   %F.type.e2e: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %F.df8: %F.type.e2e = struct_value () [template]
 // CHECK:STDOUT:   %Simple.assoc_type: type = assoc_entity_type %Simple.type [template]
 // CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, @Simple.%F.decl [template]
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%F.decl) [template]
+// CHECK:STDOUT:   %F.type.fe5: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.32d: %F.type.fe5 = struct_value () [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .Simple = %Simple.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%Simple.type] {} {}
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, <error> [template = <error>]
+// CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [template = constants.%Simple.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%F.decl) [template = constants.%impl_witness]
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: interface @Simple {
 // CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
-// CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {} {}
+// CHECK:STDOUT:   %F.decl: %F.type.e2e = fn_decl @F.1 [template = constants.%F.df8] {} {}
 // CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, %F.decl [template = constants.%assoc0]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -66,28 +88,64 @@ fn Function() {
 // CHECK:STDOUT:   witness = (%F.decl)
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: generic fn @F(@Simple.%Self: %Simple.type) {
+// CHECK:STDOUT: impl @impl: %Self.ref as %Simple.ref {
+// CHECK:STDOUT:   %F.decl: %F.type.fe5 = fn_decl @F.2 [template = constants.%F.32d] {} {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   witness = file.%impl_witness
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @F.1(@Simple.%Self: %Simple.type) {
 // CHECK:STDOUT:   fn();
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: specific @F(constants.%Self) {}
+// CHECK:STDOUT: fn @F.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @F.1(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @F.1(<error>) {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: --- fail_function.carbon
 // CHECK:STDOUT:
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %Simple.type: type = facet_type <@Simple> [template]
 // CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic]
-// CHECK:STDOUT:   %F.type: type = fn_type @F [template]
-// CHECK:STDOUT:   %F: %F.type = struct_value () [template]
+// CHECK:STDOUT:   %F.type.e2e: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %F.df8: %F.type.e2e = struct_value () [template]
 // CHECK:STDOUT:   %Simple.assoc_type: type = assoc_entity_type %Simple.type [template]
 // CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, @Simple.%F.decl [template]
+// CHECK:STDOUT:   %Function.type: type = fn_type @Function [template]
+// CHECK:STDOUT:   %Function: %Function.type = struct_value () [template]
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%F.decl) [template]
+// CHECK:STDOUT:   %F.type.bc7: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.0a2: %F.type.bc7 = struct_value () [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .Simple = %Simple.decl
+// CHECK:STDOUT:     .Function = %Function.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %Simple.decl: type = interface_decl @Simple [template = constants.%Simple.type] {} {}
+// CHECK:STDOUT:   %Function.decl: %Function.type = fn_decl @Function [template = constants.%Function] {} {}
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: interface @Simple {
 // CHECK:STDOUT:   %Self: %Simple.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
-// CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {} {}
+// CHECK:STDOUT:   %F.decl: %F.type.e2e = fn_decl @F.1 [template = constants.%F.df8] {} {}
 // CHECK:STDOUT:   %assoc0: %Simple.assoc_type = assoc_entity element0, %F.decl [template = constants.%assoc0]
 // CHECK:STDOUT:
 // CHECK:STDOUT: !members:
@@ -96,11 +154,34 @@ fn Function() {
 // CHECK:STDOUT:   witness = (%F.decl)
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: generic fn @F(@Simple.%Self: %Simple.type) {
+// CHECK:STDOUT: impl @impl: %Self.ref as %Simple.ref {
+// CHECK:STDOUT:   %F.decl: %F.type.bc7 = fn_decl @F.2 [template = constants.%F.0a2] {} {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   witness = @Function.%impl_witness
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @F.1(@Simple.%Self: %Simple.type) {
 // CHECK:STDOUT:   fn();
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: fn @Function();
+// CHECK:STDOUT: fn @Function() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, <error> [template = <error>]
+// CHECK:STDOUT:     %Simple.ref: type = name_ref Simple, file.%Simple.decl [template = constants.%Simple.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.%F.decl) [template = constants.%impl_witness]
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @F.1(constants.%Self) {}
 // CHECK:STDOUT:
-// CHECK:STDOUT: specific @F(constants.%Self) {}
+// CHECK:STDOUT: specific @F.1(<error>) {}
 // CHECK:STDOUT:
diff --git a/toolchain/check/testdata/impl/no_prelude/fail_extend_impl_scope.carbon b/toolchain/check/testdata/impl/no_prelude/fail_extend_impl_scope.carbon
index 517bd309d519f..cdf6025d226d2 100644
--- a/toolchain/check/testdata/impl/no_prelude/fail_extend_impl_scope.carbon
+++ b/toolchain/check/testdata/impl/no_prelude/fail_extend_impl_scope.carbon
@@ -36,24 +36,27 @@ fn F() {
 library "[[@TEST_NAME]]";
 
 interface Z {
-  fn Zero() -> Self;
+  fn Zero();
 
-  // CHECK:STDERR: fail_extend_impl_self_interface.carbon:[[@LINE+4]]:15: error: `impl as` can only be used in a class [ImplAsOutsideClass]
+  // CHECK:STDERR: fail_extend_impl_self_interface.carbon:[[@LINE+11]]:15: error: `impl as` can only be used in a class [ImplAsOutsideClass]
   // CHECK:STDERR:   extend impl as Z {
   // CHECK:STDERR:               ^~
   // CHECK:STDERR:
+  // CHECK:STDERR: fail_extend_impl_self_interface.carbon:[[@LINE+7]]:3: error: implementation of undefined interface Z [ImplOfUndefinedInterface]
+  // CHECK:STDERR:   extend impl as Z {
+  // CHECK:STDERR:   ^~~~~~~~~~~~~~~~~~
+  // CHECK:STDERR: fail_extend_impl_self_interface.carbon:[[@LINE-10]]:1: note: interface is currently being defined [InterfaceUndefinedWithinDefinition]
+  // CHECK:STDERR: interface Z {
+  // CHECK:STDERR: ^~~~~~~~~~~~~
+  // CHECK:STDERR:
   extend impl as Z {
-    fn Zero() -> Self {
-      return {};
-    }
+    fn Zero() {}
   }
 }
 
 class Point {
   extend impl as Z {
-    fn Zero() -> Self {
-      return {};
-    }
+    fn Zero() {}
   }
 }
 
@@ -148,27 +151,133 @@ fn F() {
 // CHECK:STDOUT: constants {
 // CHECK:STDOUT:   %Z.type: type = facet_type <@Z> [template]
 // CHECK:STDOUT:   %Self: %Z.type = bind_symbolic_name Self, 0 [symbolic]
-// CHECK:STDOUT:   %Self.as_type: type = facet_access_type %Self [symbolic]
+// CHECK:STDOUT:   %Zero.type.822: type = fn_type @Zero.1 [template]
+// CHECK:STDOUT:   %empty_tuple.type: type = tuple_type () [template]
+// CHECK:STDOUT:   %Zero.d14: %Zero.type.822 = struct_value () [template]
+// CHECK:STDOUT:   %Z.assoc_type: type = assoc_entity_type %Z.type [template]
+// CHECK:STDOUT:   %assoc0: %Z.assoc_type = assoc_entity element0, @Z.%Zero.decl [template]
+// CHECK:STDOUT:   %Zero.type.db4: type = fn_type @Zero.2, @impl.1(%Self) [symbolic]
+// CHECK:STDOUT:   %Zero.8fb: %Zero.type.db4 = struct_value () [symbolic]
+// CHECK:STDOUT:   %Point: type = class_type @Point [template]
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.2.%Zero.decl) [template]
+// CHECK:STDOUT:   %Zero.type.e33: type = fn_type @Zero.3 [template]
+// CHECK:STDOUT:   %Zero.dec: %Zero.type.e33 = struct_value () [template]
+// CHECK:STDOUT:   %Z.facet: %Z.type = facet_value %Point, %impl_witness [template]
+// CHECK:STDOUT:   %empty_struct_type: type = struct_type {} [template]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template]
+// CHECK:STDOUT:   %F.type: type = fn_type @F [template]
+// CHECK:STDOUT:   %F: %F.type = struct_value () [template]
+// CHECK:STDOUT:   %Point.val: %Point = struct_value () [template]
+// CHECK:STDOUT:   %.c37: type = fn_type_with_self_type %Zero.type.822, %Z.facet [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: file {}
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Z = %Z.decl
+// CHECK:STDOUT:     .Point = %Point.decl
+// CHECK:STDOUT:     .F = %F.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Z.decl: type = interface_decl @Z [template = constants.%Z.type] {} {}
+// CHECK:STDOUT:   %Point.decl: type = class_decl @Point [template = constants.%Point] {} {}
+// CHECK:STDOUT:   %F.decl: %F.type = fn_decl @F [template = constants.%F] {} {}
+// CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: interface @Z {
+// CHECK:STDOUT:   %Self: %Z.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
+// CHECK:STDOUT:   %Zero.decl: %Zero.type.822 = fn_decl @Zero.1 [template = constants.%Zero.d14] {} {}
+// CHECK:STDOUT:   %assoc0: %Z.assoc_type = assoc_entity element0, %Zero.decl [template = constants.%assoc0]
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, <error> [template = <error>]
+// CHECK:STDOUT:     %Z.ref: type = name_ref Z, file.%Z.decl [template = constants.%Z.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:
 // CHECK:STDOUT: !members:
-// CHECK:STDOUT:   .Self = <unexpected>.inst15
-// CHECK:STDOUT:   .Zero = <unexpected>.inst32.loc4_20
-// CHECK:STDOUT:   witness = invalid
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .Zero = %assoc0
+// CHECK:STDOUT:   witness = (%Zero.decl)
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: generic fn @Zero(<unexpected>.inst15: %Z.type) {
+// CHECK:STDOUT: generic impl @impl.1(@Z.%Self: %Z.type) {
+// CHECK:STDOUT: !definition:
 // CHECK:STDOUT:   %Self: %Z.type = bind_symbolic_name Self, 0 [symbolic = %Self (constants.%Self)]
-// CHECK:STDOUT:   %Self.as_type: type = facet_access_type %Self [symbolic = %Self.as_type (constants.%Self.as_type)]
+// CHECK:STDOUT:   %Zero.type: type = fn_type @Zero.2, @impl.1(%Self) [symbolic = %Zero.type (constants.%Zero.type.db4)]
+// CHECK:STDOUT:   %Zero: @impl.1.%Zero.type (%Zero.type.db4) = struct_value () [symbolic = %Zero (constants.%Zero.8fb)]
 // CHECK:STDOUT:
-// CHECK:STDOUT:   fn() -> @Zero.%Self.as_type (%Self.as_type);
+// CHECK:STDOUT:   impl: %Self.ref as %Z.ref {
+// CHECK:STDOUT:     %Zero.decl: @impl.1.%Zero.type (%Zero.type.db4) = fn_decl @Zero.2 [symbolic = @impl.1.%Zero (constants.%Zero.8fb)] {} {}
+// CHECK:STDOUT:
+// CHECK:STDOUT:   !members:
+// CHECK:STDOUT:     .Zero = %Zero.decl
+// CHECK:STDOUT:     witness = <error>
+// CHECK:STDOUT:   }
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
-// CHECK:STDOUT: specific @Zero(constants.%Self) {
+// CHECK:STDOUT: impl @impl.2: %Self.ref as %Z.ref {
+// CHECK:STDOUT:   %Zero.decl: %Zero.type.e33 = fn_decl @Zero.3 [template = constants.%Zero.dec] {} {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Zero = %Zero.decl
+// CHECK:STDOUT:   witness = @Point.%impl_witness
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @Point {
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%Point [template = constants.%Point]
+// CHECK:STDOUT:     %Z.ref: type = name_ref Z, file.%Z.decl [template = constants.%Z.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness (@impl.2.%Zero.decl) [template = constants.%impl_witness]
+// CHECK:STDOUT:   %complete_type: <witness> = complete_type_witness %empty_struct_type [template = constants.%complete_type]
+// CHECK:STDOUT:   complete_type_witness = %complete_type
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%Point
+// CHECK:STDOUT:   extend @impl.2.%Z.ref
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @Zero.1(@Z.%Self: %Z.type) {
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @Zero.2(@Z.%Self: %Z.type) {
+// CHECK:STDOUT: !definition:
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn() {
+// CHECK:STDOUT:   !entry:
+// CHECK:STDOUT:     return
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @Zero.3() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %.loc32_5.1: %empty_struct_type = struct_literal ()
+// CHECK:STDOUT:   %Point.ref: type = name_ref Point, file.%Point.decl [template = constants.%Point]
+// CHECK:STDOUT:   %.loc32_5.2: ref %Point = temporary_storage
+// CHECK:STDOUT:   %.loc32_5.3: init %Point = class_init (), %.loc32_5.2 [template = constants.%Point.val]
+// CHECK:STDOUT:   %.loc32_5.4: ref %Point = temporary %.loc32_5.2, %.loc32_5.3
+// CHECK:STDOUT:   %.loc32_7: ref %Point = converted %.loc32_5.1, %.loc32_5.4
+// CHECK:STDOUT:   %Zero.ref: %Z.assoc_type = name_ref Zero, @Z.%assoc0 [template = constants.%assoc0]
+// CHECK:STDOUT:   %impl.elem0: %.c37 = impl_witness_access constants.%impl_witness, element0 [template = constants.%Zero.dec]
+// CHECK:STDOUT:   %Zero.call: init %empty_tuple.type = call %impl.elem0()
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @Zero.1(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @impl.1(constants.%Self) {
+// CHECK:STDOUT: !definition:
 // CHECK:STDOUT:   %Self => constants.%Self
-// CHECK:STDOUT:   %Self.as_type => constants.%Self.as_type
+// CHECK:STDOUT:   %Zero.type => constants.%Zero.type.db4
+// CHECK:STDOUT:   %Zero => constants.%Zero.8fb
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
+// CHECK:STDOUT: specific @Zero.2(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @impl.1(%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @Zero.1(constants.%Z.facet) {}
+// CHECK:STDOUT:
diff --git a/toolchain/check/testdata/impl/no_prelude/fail_impl_bad_type.carbon b/toolchain/check/testdata/impl/no_prelude/fail_impl_bad_type.carbon
index 03a077f4f053c..0d022548e443f 100644
--- a/toolchain/check/testdata/impl/no_prelude/fail_impl_bad_type.carbon
+++ b/toolchain/check/testdata/impl/no_prelude/fail_impl_bad_type.carbon
@@ -22,7 +22,6 @@ impl true as I {}
 // CHECK:STDOUT:   %I.type: type = facet_type <@I> [template]
 // CHECK:STDOUT:   %Self: %I.type = bind_symbolic_name Self, 0 [symbolic]
 // CHECK:STDOUT:   %true: bool = bool_literal true [template]
-// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness () [template]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: file {
@@ -35,7 +34,6 @@ impl true as I {}
 // CHECK:STDOUT:     %.loc17: type = converted %true, <error> [template = <error>]
 // CHECK:STDOUT:     %I.ref: type = name_ref I, file.%I.decl [template = constants.%I.type]
 // CHECK:STDOUT:   }
-// CHECK:STDOUT:   %impl_witness: <witness> = impl_witness () [template = constants.%impl_witness]
 // CHECK:STDOUT: }
 // CHECK:STDOUT:
 // CHECK:STDOUT: interface @I {
@@ -48,6 +46,6 @@ impl true as I {}
 // CHECK:STDOUT:
 // CHECK:STDOUT: impl @impl: <error> as %I.ref {
 // CHECK:STDOUT: !members:
-// CHECK:STDOUT:   witness = file.%impl_witness
+// CHECK:STDOUT:   witness = <error>
 // CHECK:STDOUT: }
 // CHECK:STDOUT: