diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index 3ffb6ec..c1678d4 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -2423,7 +2423,7 @@
   if (getDiagnostics().hasErrorOccurred())
     return true;
 
-  std::vector<unsigned char> Buffer;
+  SmallString<128> Buffer;
   llvm::BitstreamWriter Stream(Buffer);
   ASTWriter Writer(Stream);
   // FIXME: Handle modules
diff --git a/lib/Frontend/SerializedDiagnosticPrinter.cpp b/lib/Frontend/SerializedDiagnosticPrinter.cpp
index 7a8edf7..7bf8742 100644
--- a/lib/Frontend/SerializedDiagnosticPrinter.cpp
+++ b/lib/Frontend/SerializedDiagnosticPrinter.cpp
@@ -159,7 +159,7 @@
   const DiagnosticOptions &DiagOpts;
   
   /// \brief The byte buffer for the serialized content.
-  std::vector<unsigned char> Buffer;
+  SmallString<1024> Buffer;
 
   /// \brief The BitStreamWriter for the serialized diagnostics.
   llvm::BitstreamWriter Stream;