diff --git a/clang/lib/Frontend/FrontendAction.cpp b/clang/lib/Frontend/FrontendAction.cpp
--- a/clang/lib/Frontend/FrontendAction.cpp
+++ b/clang/lib/Frontend/FrontendAction.cpp
@@ -807,12 +807,14 @@
     goto failure;
 
   // If we were asked to load any module map files, do so now.
-  for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
-    if (auto File = CI.getFileManager().getFile(Filename))
-      CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
-          *File, /*IsSystem*/false);
-    else
-      CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
+  if (CI.getLangOpts().Modules) {
+    for (const auto &Filename : CI.getFrontendOpts().ModuleMapFiles) {
+      if (auto File = CI.getFileManager().getFile(Filename))
+        CI.getPreprocessor().getHeaderSearchInfo().loadModuleMapFile(
+            *File, /*IsSystem*/ false);
+      else
+        CI.getDiagnostics().Report(diag::err_module_map_not_found) << Filename;
+    }
   }
 
   // Add a module declaration scope so that modules from -fmodule-map-file
diff --git a/clang/test/Modules/explicit-module-maps.cpp b/clang/test/Modules/explicit-module-maps.cpp
new file mode 100644
--- /dev/null
+++ b/clang/test/Modules/explicit-module-maps.cpp
@@ -0,0 +1,8 @@
+// Test that an explicit module map (which fails to parse/load in this case)
+// isn't used if modules aren't enabled.
+
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo 'DOES NOT PARSE!' > %t/invalid.modulemap
+// RUN: %clang_cc1 -fmodule-map-file=%t/invalid.modulemap -verify %s
+// expected-no-diagnostics