diff --git a/lib/Basic/DiagnosticIDs.cpp b/lib/Basic/DiagnosticIDs.cpp
index 9d460a5..9481287 100644
--- a/lib/Basic/DiagnosticIDs.cpp
+++ b/lib/Basic/DiagnosticIDs.cpp
@@ -550,9 +550,12 @@
       !MappingInfo.isUser())
     Result = DiagnosticIDs::Warning;
 
-  // Ignore any kind of extension diagnostics inside __extension__ blocks.
-  bool IsExtensionDiag = isBuiltinExtensionDiag(DiagID);
-  if (Diag.AllExtensionsSilenced && IsExtensionDiag)
+  // Ignore -pedantic diagnostics inside __extension__ blocks.
+  // (The diagnostics controlled by -pedantic are the extension diagnostics
+  // that are not enabled by default.)
+  bool EnabledByDefault;
+  bool IsExtensionDiag = isBuiltinExtensionDiag(DiagID, EnabledByDefault);
+  if (Diag.AllExtensionsSilenced && IsExtensionDiag && !EnabledByDefault)
     return DiagnosticIDs::Ignored;
 
   // For extension diagnostics that haven't been explicitly mapped, check if we