Index: lib/Sema/SemaType.cpp
===================================================================
--- lib/Sema/SemaType.cpp
+++ lib/Sema/SemaType.cpp
@@ -1679,8 +1679,9 @@
     // 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()) {
+    if (!S.getLangOpts().C99 && !S.getLangOpts().CPlusPlus &&
+        TypeQuals & Result.getCVRQualifiers() && !S.getLangOpts().GNUMode &&
+        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
@@ -3,3 +3,8 @@
 int f(int restrict);
 
 void main() {} // expected-warning {{return type of 'main' is not 'int'}} expected-note {{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; // expected-warning {{extension used}}