diff --git a/clang/include/clang/Frontend/ASTUnit.h b/clang/include/clang/Frontend/ASTUnit.h
index 471476a44477..970866469f1f 100644
--- a/clang/include/clang/Frontend/ASTUnit.h
+++ b/clang/include/clang/Frontend/ASTUnit.h
@@ -559,17 +559,26 @@ public:
   }
   
   // Retrieve the diagnostics associated with this AST
-  typedef const StoredDiagnostic *stored_diag_iterator;
-  stored_diag_iterator stored_diag_begin() const { 
+  typedef StoredDiagnostic *stored_diag_iterator;
+  typedef const StoredDiagnostic *stored_diag_const_iterator;
+  stored_diag_const_iterator stored_diag_begin() const { 
     return StoredDiagnostics.begin(); 
   }
-  stored_diag_iterator stored_diag_end() const { 
+  stored_diag_iterator stored_diag_begin() { 
+    return StoredDiagnostics.begin(); 
+  }
+  stored_diag_const_iterator stored_diag_end() const { 
+    return StoredDiagnostics.end(); 
+  }
+  stored_diag_iterator stored_diag_end() { 
     return StoredDiagnostics.end(); 
   }
   unsigned stored_diag_size() const { return StoredDiagnostics.size(); }
-  
-  SmallVector<StoredDiagnostic, 4> &getStoredDiagnostics() { 
-    return StoredDiagnostics; 
+
+  stored_diag_iterator stored_diag_afterDriver_begin() {
+    if (NumStoredDiagnosticsFromDriver > StoredDiagnostics.size())
+      NumStoredDiagnosticsFromDriver = 0;
+    return StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver; 
   }
 
   typedef std::vector<CachedCodeCompletionResult>::iterator
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 032adf3876a4..c1534352253c 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -919,9 +919,7 @@ bool ASTUnit::Parse(llvm::MemoryBuffer *OverrideMainBuffer) {
   CleanTemporaryFiles();
 
   if (!OverrideMainBuffer) {
-    StoredDiagnostics.erase(
-                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
-                            StoredDiagnostics.end());
+    StoredDiagnostics.erase(stored_diag_afterDriver_begin(), stored_diag_end());
     TopLevelDeclsInPreamble.clear();
   }
 
@@ -1002,6 +1000,7 @@ error:
   }
   
   StoredDiagnostics.clear();
+  NumStoredDiagnosticsFromDriver = 0;
   return true;
 }
 
@@ -1393,9 +1392,7 @@ llvm::MemoryBuffer *ASTUnit::getMainBufferWithPrecompiledPreamble(
   // Clear out old caches and data.
   getDiagnostics().Reset();
   ProcessWarningOptions(getDiagnostics(), Clang->getDiagnosticOpts());
-  StoredDiagnostics.erase(
-                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
-                          StoredDiagnostics.end());
+  StoredDiagnostics.erase(stored_diag_afterDriver_begin(), stored_diag_end());
   TopLevelDecls.clear();
   TopLevelDeclsInPreamble.clear();
   
@@ -1438,11 +1435,8 @@ llvm::MemoryBuffer *ASTUnit::getMainBufferWithPrecompiledPreamble(
   // of preamble diagnostics.
   PreambleDiagnostics.clear();
   PreambleDiagnostics.insert(PreambleDiagnostics.end(), 
-                   StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
-                             StoredDiagnostics.end());
-  StoredDiagnostics.erase(
-                    StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver,
-                          StoredDiagnostics.end());
+                            stored_diag_afterDriver_begin(), stored_diag_end());
+  StoredDiagnostics.erase(stored_diag_afterDriver_begin(), stored_diag_end());
   
   // Keep track of the preamble we precompiled.
   PreambleFile = FrontendOpts.OutputFile;
@@ -2196,8 +2190,8 @@ void ASTUnit::CodeComplete(StringRef File, unsigned Line, unsigned Column,
   // make that override happen and introduce the preamble.
   PreprocessorOpts.DisableStatCache = true;
   StoredDiagnostics.insert(StoredDiagnostics.end(),
-                           this->StoredDiagnostics.begin(),
-             this->StoredDiagnostics.begin() + NumStoredDiagnosticsFromDriver);
+                           stored_diag_begin(),
+                           stored_diag_afterDriver_begin());
   if (OverrideMainBuffer) {
     PreprocessorOpts.addRemappedFile(OriginalSourceFile, OverrideMainBuffer);
     PreprocessorOpts.PrecompiledPreambleBytes.first = Preamble.size();