diff --git a/clang/include/clang/AST/DeclContextInternals.h b/clang/include/clang/AST/DeclContextInternals.h
index 903cdb7bfcc822..c4734ab5789538 100644
--- a/clang/include/clang/AST/DeclContextInternals.h
+++ b/clang/include/clang/AST/DeclContextInternals.h
@@ -205,7 +205,7 @@ class StoredDeclsList {
     Data.setPointer(Head);
   }
 
-  /// Return an array of all the decls that this list represents.
+  /// Return the list of all the decls.
   DeclContext::lookup_result getLookupResult() const {
     return DeclContext::lookup_result(Data.getPointer());
   }
diff --git a/clang/lib/Interpreter/IncrementalParser.cpp b/clang/lib/Interpreter/IncrementalParser.cpp
index 370bcbfee8b014..5eec2a2fd6d1a6 100644
--- a/clang/lib/Interpreter/IncrementalParser.cpp
+++ b/clang/lib/Interpreter/IncrementalParser.cpp
@@ -375,16 +375,22 @@ void IncrementalParser::CleanUpPTU(PartialTranslationUnit &PTU) {
   TranslationUnitDecl *MostRecentTU = PTU.TUPart;
   TranslationUnitDecl *FirstTU = MostRecentTU->getFirstDecl();
   if (StoredDeclsMap *Map = FirstTU->getPrimaryContext()->getLookupPtr()) {
-    for (auto I = Map->begin(); I != Map->end(); ++I) {
-      StoredDeclsList &List = I->second;
+    for (auto &&[Key, List] : *Map) {
       DeclContextLookupResult R = List.getLookupResult();
+      std::vector<NamedDecl *> NamedDeclsToRemove;
+      bool RemoveAll = true;
       for (NamedDecl *D : R) {
-        if (D->getTranslationUnitDecl() == MostRecentTU) {
+        if (D->getTranslationUnitDecl() == MostRecentTU)
+          NamedDeclsToRemove.push_back(D);
+        else
+          RemoveAll = false;
+      }
+      if (LLVM_LIKELY(RemoveAll)) {
+        Map->erase(Key);
+      } else {
+        for (NamedDecl *D : NamedDeclsToRemove)
           List.remove(D);
-        }
       }
-      if (List.isNull())
-        Map->erase(I);
     }
   }
 }