diff --git a/include/clang/Basic/LangOptions.def b/include/clang/Basic/LangOptions.def
index 215e462..954deaa 100644
--- a/include/clang/Basic/LangOptions.def
+++ b/include/clang/Basic/LangOptions.def
@@ -254,6 +254,7 @@
 LANGOPT(RetainCommentsFromSystemHeaders, 1, 0, "retain documentation comments from system headers in the AST")
 LANGOPT(APINotes, 1, 0, "use external API notes")
 LANGOPT(APINotesModules, 1, 0, "use external API notes")
+LANGOPT(NeededByPCHOrCompilationUsesPCH, 1, 0, "compilation involves pch")
 
 LANGOPT(SanitizeAddressFieldPadding, 2, 0, "controls how aggressive is ASan "
                                            "field padding (0: none, 1:least "
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index c9290a5..9805c15 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -1751,7 +1751,7 @@
     if (!AST)
       return nullptr;
   }
-  
+
   if (!ResourceFilesPath.empty()) {
     // Override the resources path.
     CI->getHeaderSearchOpts().ResourceDir = ResourceFilesPath;
@@ -1984,6 +1984,9 @@
   if (ModuleFormat)
     CI->getHeaderSearchOpts().ModuleFormat = ModuleFormat.getValue();
 
+  if (ForSerialization)
+    CI->getLangOpts()->NeededByPCHOrCompilationUsesPCH = true;
+
   // Create the AST unit.
   std::unique_ptr<ASTUnit> AST;
   AST.reset(new ASTUnit(false));
diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index b79e118..b391950 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -2460,6 +2460,10 @@
   ParsePreprocessorOutputArgs(Res.getPreprocessorOutputOpts(), Args,
                               Res.getFrontendOpts().ProgramAction);
 
+  if (!Res.getPreprocessorOpts().ImplicitPCHInclude.empty() ||
+      Res.getFrontendOpts().ProgramAction == frontend::GeneratePCH)
+    LangOpts.NeededByPCHOrCompilationUsesPCH = true;
+
   // Turn on -Wspir-compat for SPIR target.
   llvm::Triple T(Res.getTargetOpts().Triple);
   auto Arch = T.getArch();
diff --git a/lib/Frontend/FrontendAction.cpp b/lib/Frontend/FrontendAction.cpp
index 9eb08a5..da1ab7b 100644
--- a/lib/Frontend/FrontendAction.cpp
+++ b/lib/Frontend/FrontendAction.cpp
@@ -297,6 +297,7 @@
                 CI.getLangOpts(), CI.getTargetOpts(), CI.getPreprocessorOpts(),
                 SpecificModuleCachePath)) {
           PPOpts.ImplicitPCHInclude = Dir->getName();
+          CI.getLangOpts().NeededByPCHOrCompilationUsesPCH = true;
           Found = true;
           break;
         }
diff --git a/lib/Serialization/ASTReader.cpp b/lib/Serialization/ASTReader.cpp
index 9d50f7a..0461a53 100644
--- a/lib/Serialization/ASTReader.cpp
+++ b/lib/Serialization/ASTReader.cpp
@@ -4045,7 +4045,7 @@
   }
 
   // FIXME: Should we check the signature even if DisableValidation?
-  if (DisableValidation ||
+  if (PP.getLangOpts().NeededByPCHOrCompilationUsesPCH || DisableValidation ||
       (AllowConfigurationMismatch && Result == ConfigurationMismatch))
     return Success;
 
diff --git a/test/Modules/explicit-build.cpp b/test/Modules/explicit-build.cpp
index a6f6a62..087cba5 100644
--- a/test/Modules/explicit-build.cpp
+++ b/test/Modules/explicit-build.cpp
@@ -150,7 +150,7 @@
 // RUN:            -fmodule-file=%t/a.pch \
 // RUN:            %s 2>&1 | FileCheck --check-prefix=CHECK-A-AS-PCH %s
 //
-// CHECK-A-AS-PCH: fatal error: AST file '{{.*}}a.pch' was not built as a module
+// CHECK-A-AS-PCH: error: module file {{.*}}a.pch cannot be loaded due to a configuration mismatch with the current compilation
 
 // -------------------------------
 // Try to import a non-AST file with -fmodule-file=