Index: clang/lib/Basic/DiagnosticIDs.cpp
===================================================================
--- clang/lib/Basic/DiagnosticIDs.cpp
+++ clang/lib/Basic/DiagnosticIDs.cpp
@@ -396,6 +396,14 @@
   return toLevel(getDiagnosticSeverity(DiagID, Loc, Diag));
 }
 
+static bool isSystemFunctionMacroBodyExpansion(SourceLocation Loc,
+                                               const SourceManager &SM) {
+  if (!(SM.isInSystemMacro(Loc) && SM.isMacroBodyExpansion(Loc)))
+    return false;
+  auto Range = SM.getImmediateExpansionRange(Loc);
+  return Range.first != Range.second;
+}
+
 /// \brief Based on the way the client configured the Diagnostic
 /// object, classify the specified diagnostic ID into a Level, consumable by
 /// the DiagnosticClient.
@@ -469,8 +477,10 @@
   // because we also want to ignore extensions and warnings in -Werror and
   // -pedantic-errors modes, which *map* warnings/extensions to errors.
   if (State->SuppressSystemWarnings && !ShowInSystemHeader && Loc.isValid() &&
-      Diag.getSourceManager().isInSystemHeader(
-          Diag.getSourceManager().getExpansionLoc(Loc)))
+      (Diag.getSourceManager().isInSystemHeader(
+          Diag.getSourceManager().getExpansionLoc(Loc)) ||
+       (IsExtensionDiag &&
+        isSystemFunctionMacroBodyExpansion(Loc, Diag.getSourceManager()))))
     return diag::Severity::Ignored;
 
   return Result;
Index: clang/test/SemaCXX/warn-sysheader-macro.cpp
===================================================================
--- clang/test/SemaCXX/warn-sysheader-macro.cpp
+++ clang/test/SemaCXX/warn-sysheader-macro.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -verify -fsyntax-only -Wshadow -Wold-style-cast %s
+// RUN: %clang_cc1 -verify -fsyntax-only -Wshadow -Wold-style-cast -pedantic %s
 
 // Test that macro expansions from system headers don't trigger 'syntactic'
 // warnings that are not actionable.
@@ -12,6 +12,8 @@
 
 #define OLD_STYLE_CAST(a) ((int) (a))
 
+#define ASSERT(a) ({ if (a) {} else {} })
+
 #else
 
 #define IS_SYSHEADER
@@ -32,4 +34,9 @@
   int i = OLD_STYLE_CAST(0);
 }
 
+void testExtension() {
+  ASSERT(true);
+  ASSERT(({ true; })); // expected-warning {{use of GNU statement expression extension}}
+}
+
 #endif