diff --git a/clang/lib/Lex/ModuleMap.cpp b/clang/lib/Lex/ModuleMap.cpp
index 9554d3b..d619b52 100644
--- a/clang/lib/Lex/ModuleMap.cpp
+++ b/clang/lib/Lex/ModuleMap.cpp
@@ -359,6 +359,13 @@
     return MakeResult(Result);
   }
 
+  return MakeResult(findOrCreateModuleForHeaderInUmbrellaDir(File));
+}
+
+ModuleMap::KnownHeader
+ModuleMap::findOrCreateModuleForHeaderInUmbrellaDir(const FileEntry *File) {
+  assert(!Headers.count(File) && "already have a module for this header");
+
   SmallVector<const DirectoryEntry *, 2> SkippedDirs;
   KnownHeader H = findHeaderInUmbrellaDirs(File, SkippedDirs);
   if (H) {
@@ -419,19 +426,22 @@
         UmbrellaDirs[SkippedDirs[I]] = Result;
     }
 
-    Headers[File].push_back(KnownHeader(Result, NormalHeader));
-
-    // If a header corresponds to an unavailable module, don't report
-    // that it maps to anything.
-    if (!Result->isAvailable())
-      return KnownHeader();
-
-    return MakeResult(Headers[File].back());
+    KnownHeader Header(Result, NormalHeader);
+    Headers[File].push_back(Header);
+    return Header;
   }
 
   return KnownHeader();
 }
 
+ArrayRef<ModuleMap::KnownHeader>
+ModuleMap::findAllModulesForHeader(const FileEntry *File) const {
+  auto It = Headers.find(File);
+  if (It == Headers.end())
+    return None;
+  return It->second;
+}
+
 bool ModuleMap::isHeaderInUnavailableModule(const FileEntry *Header) const {
   return isHeaderUnavailableInModule(Header, nullptr);
 }
@@ -787,14 +797,21 @@
 
 void ModuleMap::addHeader(Module *Mod, Module::Header Header,
                           ModuleHeaderRole Role) {
-  if (!(Role & TextualHeader)) {
-    bool isCompilingModuleHeader = Mod->getTopLevelModule() == CompilingModule;
-    HeaderInfo.MarkFileModuleHeader(Header.Entry, Role,
-                                    isCompilingModuleHeader);
-  }
-  Headers[Header.Entry].push_back(KnownHeader(Mod, Role));
+  KnownHeader KH(Mod, Role);
 
+  // Only add each header to the headers list once.
+  // FIXME: Should we diagnose if a header is listed twice in the
+  // same module definition?
+  auto &HeaderList = Headers[Header.Entry];
+  for (auto H : HeaderList)
+    if (H == KH)
+      return;
+
+  HeaderList.push_back(KH);
   Mod->Headers[headerRoleToKind(Role)].push_back(std::move(Header));
+
+  bool isCompilingModuleHeader = Mod->getTopLevelModule() == CompilingModule;
+  HeaderInfo.MarkFileModuleHeader(Header.Entry, Role, isCompilingModuleHeader);
 }
 
 void ModuleMap::excludeHeader(Module *Mod, Module::Header Header) {