diff --git a/lib/Frontend/CompilerInstance.cpp b/lib/Frontend/CompilerInstance.cpp
index 0e60c39..a7f0770 100644
--- a/lib/Frontend/CompilerInstance.cpp
+++ b/lib/Frontend/CompilerInstance.cpp
@@ -61,7 +61,9 @@
 }
 
 bool CompilerInstance::shouldBuildGlobalModuleIndex() const {
-  return BuildGlobalModuleIndex && !ModuleBuildFailed;
+  return (BuildGlobalModuleIndex ||
+          (ModuleManager && ModuleManager->isGlobalIndexUnavailable())) &&
+         !ModuleBuildFailed;
 }
 
 void CompilerInstance::setDiagnostics(DiagnosticsEngine *Value) {