Index: clang/lib/Basic/Diagnostic.cpp
===================================================================
--- clang/lib/Basic/Diagnostic.cpp
+++ clang/lib/Basic/Diagnostic.cpp
@@ -374,6 +374,12 @@
   DiagnosticMapping Mapping = makeUserMapping(Map, L);
   Mapping.setUpgradedFromWarning(WasUpgradedFromWarning);
 
+  // Make sure we propagate the NoWarningAsError flag from an existing
+  // mapping (which may be the default mapping).
+  DiagnosticMapping &Info = GetCurDiagState()->getOrAddMapping(Diag);
+  Mapping.setNoWarningAsError(Info.hasNoWarningAsError() ||
+                              Mapping.hasNoWarningAsError());
+
   // Common case; setting all the diagnostics of a group in one place.
   if ((L.isInvalid() || L == DiagStatesByLoc.getCurDiagStateLoc()) &&
       DiagStatesByLoc.getCurDiagState()) {
Index: clang/test/Lexer/pragma-message.c
===================================================================
--- clang/test/Lexer/pragma-message.c
+++ clang/test/Lexer/pragma-message.c
@@ -8,24 +8,25 @@
 // #pragma message messagestring
 //
 // RUN: %clang_cc1 -fsyntax-only -verify -Werror %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Werror -W#pragma-messages %s
 #define STRING2(x) #x
 #define STRING(x) STRING2(x)
-#pragma message(":O I'm a message! " STRING(__LINE__)) // expected-warning {{:O I'm a message! 13}}
-#pragma message ":O gcc accepts this! " STRING(__LINE__) // expected-warning {{:O gcc accepts this! 14}}
+#pragma message(":O I'm a message! " STRING(__LINE__)) // expected-warning {{:O I'm a message! 14}}
+#pragma message ":O gcc accepts this! " STRING(__LINE__) // expected-warning {{:O gcc accepts this! 15}}
 
 #pragma message(invalid) // expected-error {{expected string literal in pragma message}}
 
 // GCC supports a similar pragma, #pragma GCC warning (which generates a warning
 // message) and #pragma GCC error (which generates an error message).
 
-#pragma GCC warning(":O I'm a message! " STRING(__LINE__)) // expected-warning {{:O I'm a message! 21}}
-#pragma GCC warning ":O gcc accepts this! " STRING(__LINE__) // expected-warning {{:O gcc accepts this! 22}}
+#pragma GCC warning(":O I'm a message! " STRING(__LINE__)) // expected-warning {{:O I'm a message! 22}}
+#pragma GCC warning ":O gcc accepts this! " STRING(__LINE__) // expected-warning {{:O gcc accepts this! 23}}
 
-#pragma GCC error(":O I'm a message! " STRING(__LINE__)) // expected-error {{:O I'm a message! 24}}
-#pragma GCC error ":O gcc accepts this! " STRING(__LINE__) // expected-error {{:O gcc accepts this! 25}}
+#pragma GCC error(":O I'm a message! " STRING(__LINE__)) // expected-error {{:O I'm a message! 25}}
+#pragma GCC error ":O gcc accepts this! " STRING(__LINE__) // expected-error {{:O gcc accepts this! 26}}
 
 #define COMPILE_ERROR(x) _Pragma(STRING2(GCC error(x)))
-COMPILE_ERROR("Compile error at line " STRING(__LINE__) "!"); // expected-error {{Compile error at line 28!}}
+COMPILE_ERROR("Compile error at line " STRING(__LINE__) "!"); // expected-error {{Compile error at line 29!}}
 
 #pragma message // expected-error {{pragma message requires parenthesized string}}
 #pragma GCC warning("" // expected-error {{pragma warning requires parenthesized string}}