diff --git a/clang/Parse/ParseStmt.cpp b/clang/Parse/ParseStmt.cpp
index 8715686e429b..c800ad0e1ff4 100644
--- a/clang/Parse/ParseStmt.cpp
+++ b/clang/Parse/ParseStmt.cpp
@@ -267,6 +267,8 @@ void Parser::ParseForStatement() {
     ConsumeToken();
   } else if (isDeclarationSpecifier()) {  // for (int X = 4;
     // Parse declaration, which eats the ';'.
+    if (!getLang().C99)   // Use of C99-style for loops in C90 mode?
+      Diag(Tok, diag::ext_c99_variable_decl_in_for_loop);
     ParseDeclaration(Declarator::ForContext);
   } else {
     ParseExpression();
diff --git a/clang/include/clang/Basic/DiagnosticKinds.def b/clang/include/clang/Basic/DiagnosticKinds.def
index 4e910476e688..c7b0e418b20f 100644
--- a/clang/include/clang/Basic/DiagnosticKinds.def
+++ b/clang/include/clang/Basic/DiagnosticKinds.def
@@ -254,6 +254,8 @@ DIAG(ext_ident_list_in_param, EXTENSION,
      "type-less parameter names in function declaration")
 DIAG(ext_c99_array_usage, EXTENSION,
      "use of c99-specific array features")
+DIAG(ext_c99_variable_decl_in_for_loop, EXTENSION,
+     "variable declaration in for loop is a c99-specific feature")
 
 // Generic errors.
 DIAG(err_parse_error, ERROR,