diff --git a/lib/AST/SubstitutionMap.cpp b/lib/AST/SubstitutionMap.cpp
index c5588a9767b15..8204ab20f5ad9 100644
--- a/lib/AST/SubstitutionMap.cpp
+++ b/lib/AST/SubstitutionMap.cpp
@@ -283,20 +283,6 @@ SubstitutionMap::lookupConformance(CanType type, ProtocolDecl *proto) const {
 
   // For each remaining step, project an associated conformance.
   while (iter != path.end()) {
-    // FIXME: Remove this hack. It is unsound, because we may not have diagnosed
-    // anything but still end up with an ErrorType in the AST.
-    if (conformance.isConcrete()) {
-      auto concrete = conformance.getConcrete();
-      if (auto normal = dyn_cast<NormalProtocolConformance>(concrete->getRootConformance())) {
-        if (!normal->hasComputedAssociatedConformances()) {
-          if (proto->getASTContext().evaluator.hasActiveRequest(
-                ResolveTypeWitnessesRequest{normal})) {
-            return ProtocolConformanceRef::forInvalid();
-          }
-        }
-      }
-    }
-
     const auto step = *iter++;
     conformance = conformance.getAssociatedConformance(step.first, step.second);
   }
diff --git a/lib/AST/TypeSubstitution.cpp b/lib/AST/TypeSubstitution.cpp
index 2c04ea3de0517..ab8d1ddfeaf5c 100644
--- a/lib/AST/TypeSubstitution.cpp
+++ b/lib/AST/TypeSubstitution.cpp
@@ -358,7 +358,7 @@ class TypeSubstituter : public TypeTransform<TypeSubstituter> {
   std::optional<Type> transformLocalArchetypeType(LocalArchetypeType *local,
                                                   TypePosition pos);
 
-  // SubstitutionMap transformSubstitutionMap(SubstitutionMap subs);
+  SubstitutionMap transformSubstitutionMap(SubstitutionMap subs);
 
   CanType transformSILField(CanType fieldTy, TypePosition pos);
 };
@@ -474,13 +474,10 @@ Type TypeSubstituter::transformDependentMemberType(DependentMemberType *dependen
   return result;
 }
 
-// FIXME: This exposes a scalability issue; see test/SILGen/opaque_result_type_slow.swift.
-/*
 SubstitutionMap TypeSubstituter::transformSubstitutionMap(SubstitutionMap subs) {
   // FIXME: Take level into account? Move level down into IFS?
   return subs.subst(IFS);
 }
-*/
 
 CanType TypeSubstituter::transformSILField(CanType fieldTy, TypePosition pos) {
   // Type substitution does not walk into the SILBoxType's field types, because
diff --git a/validation-test/compiler_crashers_2/174f557922f5c3cc.swift b/validation-test/compiler_crashers_2_fixed/174f557922f5c3cc.swift
similarity index 89%
rename from validation-test/compiler_crashers_2/174f557922f5c3cc.swift
rename to validation-test/compiler_crashers_2_fixed/174f557922f5c3cc.swift
index bb3d379def568..72c539f629e14 100644
--- a/validation-test/compiler_crashers_2/174f557922f5c3cc.swift
+++ b/validation-test/compiler_crashers_2_fixed/174f557922f5c3cc.swift
@@ -1,5 +1,5 @@
 // {"kind":"typecheck","original":"2fdf1565","signature":"(anonymous namespace)::TypeSubstituter::transformDependentMemberType(swift::DependentMemberType*, swift::TypePosition)","stackOverflow":true}
-// RUN: not --crash %target-swift-frontend -typecheck %s
+// RUN: not %target-swift-frontend -typecheck %s
 protocol a {
   typealias b = c
   associatedtype d: b