Index: clang/lib/Serialization/ASTReader.cpp
===================================================================
--- clang/lib/Serialization/ASTReader.cpp
+++ clang/lib/Serialization/ASTReader.cpp
@@ -2175,7 +2175,8 @@
   bool IsOutOfDate = false;
 
   // For an overridden file, there is nothing to validate.
-  if (!Overridden && //
+  // Don't emit file modification error if we have -fno-validate-pch
+  if (!Overridden && !PP.getPreprocessorOpts().DisablePCHValidation &&
       (StoredSize != File->getSize() ||
        (StoredTime && StoredTime != File->getModificationTime() &&
         !DisableValidation)
Index: clang/test/Modules/module-file-novalidate.c
===================================================================
--- /dev/null
+++ clang/test/Modules/module-file-novalidate.c
@@ -0,0 +1,11 @@
+// RUN: rm -rf %t
+// RUN: mkdir %t
+// RUN: echo 'int foo = 0;' > %t/a.h
+// RUN: echo 'module A { header "a.h" }' > %t/m.modulemap
+// RUN: %clang_cc1 -fmodules -emit-module -fmodule-name=A -x c %t/m.modulemap -o %t/m.pcm
+// RUN: echo 'int bar;' > %t/a.h
+// RUN: not %clang_cc1 -fmodules -fmodule-file=%t/m.pcm -fmodule-map-file=%t/m.modulemap -fno-validate-pch -x c %s -I%t -fsyntax-only 2>&1 | FileCheck %s
+#include "a.h"
+int foo = 0; // redefinition of 'foo'
+// CHECK-NOT: fatal error: file {{.*}} has been modified since the module file {{.*}} was built
+// REQUIRES: shell