Index: llvm/trunk/include/llvm/Support/Timer.h
===================================================================
--- llvm/trunk/include/llvm/Support/Timer.h
+++ llvm/trunk/include/llvm/Support/Timer.h
@@ -207,6 +207,8 @@
   /// This static method prints all timers and clears them all out.
   static void printAll(raw_ostream &OS);
 
+  const char *printJSONValues(raw_ostream &OS, const char *delim);
+
   /// Prints all timers as JSON key/value pairs, and clears them all out.
   static const char *printAllJSONValues(raw_ostream &OS, const char *delim);
 
@@ -223,7 +225,6 @@
   void PrintQueuedTimers(raw_ostream &OS);
   void printJSONValue(raw_ostream &OS, const PrintRecord &R,
                       const char *suffix, double Value);
-  const char *printJSONValues(raw_ostream &OS, const char *delim);
 };
 
 } // end namespace llvm
Index: llvm/trunk/lib/Support/Timer.cpp
===================================================================
--- llvm/trunk/lib/Support/Timer.cpp
+++ llvm/trunk/lib/Support/Timer.cpp
@@ -378,6 +378,8 @@
 }
 
 const char *TimerGroup::printJSONValues(raw_ostream &OS, const char *delim) {
+  sys::SmartScopedLock<true> L(*TimerLock);
+
   prepareToPrintList();
   for (const PrintRecord &R : TimersToPrint) {
     OS << delim;