Index: lib/Sema/SemaType.cpp
===================================================================
--- lib/Sema/SemaType.cpp
+++ lib/Sema/SemaType.cpp
@@ -1679,8 +1679,14 @@
     // C90 6.5.3 constraints: "The same type qualifier shall not appear more
     // than once in the same specifier-list or qualifier-list, either directly
     // or via one or more typedefs."
-    if (!S.getLangOpts().C99 && !S.getLangOpts().CPlusPlus
-        && TypeQuals & Result.getCVRQualifiers()) {
+    //
+    // Not checked for gnu89 if the TST is from a typeof expression and
+    // -pedantic was not set.
+    if (!S.getLangOpts().C99 && !S.getLangOpts().CPlusPlus &&
+        TypeQuals & Result.getCVRQualifiers() &&
+        !(S.getLangOpts().GNUMode &&
+        !S.Diags.getDiagnosticOptions().Pedantic &&
+        DS.getTypeSpecType() == DeclSpec::TST_typeofExpr))  {
       if (TypeQuals & DeclSpec::TQ_const && Result.isConstQualified()) {
         S.Diag(DS.getConstSpecLoc(), diag::ext_duplicate_declspec)
           << "const";
Index: test/Sema/gnu89.c
===================================================================
--- test/Sema/gnu89.c
+++ test/Sema/gnu89.c
@@ -1,5 +1,24 @@
-// RUN: %clang_cc1 %s -std=gnu89 -pedantic -fsyntax-only -verify
+// RUN: %clang_cc1 %s -std=gnu89 -pedantic -fsyntax-only 2>&1 | FileCheck -check-prefix=CHECK-PEDANTIC %s
+// RUN: %clang_cc1 %s -std=gnu89 -fsyntax-only 2>&1 | FileCheck %s
 
 int f(int restrict);
 
-void main() {} // expected-warning {{return type of 'main' is not 'int'}} expected-note {{change return type to 'int'}}
+void main() {}
+// CHECK: return type of 'main' is not 'int'
+// CHECK: change return type to 'int'
+
+// Do not warn about duplicate const declaration specifier as the result of
+// typeof in gnu89.
+const int c_i;
+const typeof(c_i) c_i3;
+// CHECK-PEDANTIC: warning: extension used
+// CHECK-PEDANTIC: warning: duplicate 'const' declaration specifier
+// CHECK-otherwise-NOT: warning: duplicate 'const' declaration specifier
+
+const const int x;
+// CHECK: warning: duplicate 'const' declaration specifier
+
+typedef const int t;
+const t x2;
+// CHECK: warning: duplicate 'const' declaration specifier
+