diff --git a/clang/lib/Parse/ParseAST.cpp b/clang/lib/Parse/ParseAST.cpp
index d1c2624..3f86c4d 100644
--- a/clang/lib/Parse/ParseAST.cpp
+++ b/clang/lib/Parse/ParseAST.cpp
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Parse/ParseAST.h"
+#include "clang/Parse/ParseDiagnostic.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "clang/Sema/SemaConsumer.h"
@@ -77,27 +78,50 @@
   S.getPreprocessor().EnterMainSourceFile();
   P.Initialize();
   S.Initialize();
-  
-  if (ExternalASTSource *External = S.getASTContext().getExternalSource())
+
+  // C11 6.9p1 says translation units must have at least one top-level
+  // declaration. C++ doesn't have this restriction. We also don't want to
+  // complain if we have a precompiled header, although technically if the PCH
+  // is empty we should still emit the (pedantic) diagnostic.
+  bool WarnForEmptyTU = !S.getLangOpts().CPlusPlus;
+  if (ExternalASTSource *External = S.getASTContext().getExternalSource()) {
     External->StartTranslationUnit(Consumer);
-  
-  bool Abort = false;
+    WarnForEmptyTU = false;
+  }
+
+  // Clang's predefines contain top-level declarations for things like va_list,
+  // making it hard to tell if the /user's/ translation unit has at least one
+  // top-level declaration. So we parse cautiously, looking for a declaration
+  // that doesn't come from our predefines.
+  // Note that ParseTopLevelDecl returns 'true' at EOF.
+  SourceManager &SM = S.getSourceManager();
   Parser::DeclGroupPtrTy ADecl;
-  
-  while (!P.ParseTopLevelDecl(ADecl)) {  // Not end of file.
-    // If we got a null return and something *was* parsed, ignore it.  This
-    // is due to a top-level semicolon, an action override, or a parse error
-    // skipping something.
+  while (WarnForEmptyTU && !P.ParseTopLevelDecl(ADecl)) {
     if (ADecl) {
-      if (!Consumer->HandleTopLevelDecl(ADecl.get())) {
-        Abort = true;
-        break;
+      if (!Consumer->HandleTopLevelDecl(ADecl.get()))
+        return;
+      if (DeclGroupRef::iterator FirstDecl = ADecl.get().begin()) {
+        SourceLocation DeclLoc = (*FirstDecl)->getLocation();
+        WarnForEmptyTU = SM.isFromPredefines(DeclLoc);
       }
     }
-  };
+  }
 
-  if (Abort)
-    return;
+  // If we ended up seeing EOF before any top-level declarations, emit our
+  // diagnostic. Otherwise, parse the rest of the file normally.
+  if (WarnForEmptyTU) {
+    P.Diag(diag::ext_empty_translation_unit);
+  } else {
+    while (!P.ParseTopLevelDecl(ADecl)) {  // Not end of file.
+      // If we got a null return and something *was* parsed, ignore it.  This
+      // is due to a top-level semicolon, an action override, or a parse error
+      // skipping something.
+      if (ADecl) {
+        if (!Consumer->HandleTopLevelDecl(ADecl.get())) 
+          return;
+      }
+    };
+  }
   
   // Process any TopLevelDecls generated by #pragma weak.
   for (SmallVector<Decl*,2>::iterator