diff --git a/lib/AST/Module.cpp b/lib/AST/Module.cpp
index 70422d58c781f..1915a78dee61d 100644
--- a/lib/AST/Module.cpp
+++ b/lib/AST/Module.cpp
@@ -276,8 +276,11 @@ void SourceLookupCache::populateMemberCache(const ModuleDecl &Mod) {
                              "populate-module-class-member-cache");
 
   for (const FileUnit *file : Mod.getFiles()) {
-    auto &SF = *cast<SourceFile>(file);
-    addToMemberCache(SF.getTopLevelDecls());
+    assert(isa<SourceFile>(file) ||
+           isa<SynthesizedFileUnit>(file));
+    SmallVector<Decl *, 8> decls;
+    file->getTopLevelDecls(decls);
+    addToMemberCache(decls);
   }
 
   MemberCachePopulated = true;
diff --git a/lib/FrontendTool/FrontendTool.cpp b/lib/FrontendTool/FrontendTool.cpp
index 46d5307bbd4a0..4d77daf57d5cb 100644
--- a/lib/FrontendTool/FrontendTool.cpp
+++ b/lib/FrontendTool/FrontendTool.cpp
@@ -1494,9 +1494,19 @@ static bool performCompileStepsPostSILGen(CompilerInstance &Instance,
     SerializationOptions serializationOpts =
         Invocation.computeSerializationOptions(outs, Instance.getMainModule());
 
+    // Infer if this is an emit-module job part of an incremental build,
+    // vs a partial emit-module job (with primary files) or other kinds.
+    // We may want to rely on a flag instead to differentiate them.
+    const bool isEmitModuleSeparately =
+        Action == FrontendOptions::ActionType::EmitModuleOnly &&
+        MSF.is<ModuleDecl *>() &&
+        Instance.getInvocation()
+            .getTypeCheckerOptions()
+            .SkipFunctionBodies == FunctionBodySkipping::NonInlinableWithoutTypes;
     const bool canEmitIncrementalInfoIntoModule =
         !serializationOpts.DisableCrossModuleIncrementalInfo &&
-        (Action == FrontendOptions::ActionType::MergeModules);
+        (Action == FrontendOptions::ActionType::MergeModules ||
+         isEmitModuleSeparately);
     if (canEmitIncrementalInfoIntoModule) {
       const auto alsoEmitDotFile =
           Instance.getInvocation()