diff --git a/gtsam/base/debug.cpp b/gtsam/base/debug.cpp
index e50e3af35..6abc98642 100644
--- a/gtsam/base/debug.cpp
+++ b/gtsam/base/debug.cpp
@@ -17,9 +17,32 @@
  */
 
 #include <gtsam/base/debug.h>
+#ifdef GTSAM_USE_TBB
+#include <tbb/mutex.h>
+#endif
 
 namespace gtsam {
 
-  GTSAM_EXPORT FastMap<std::string, ValueWithDefault<bool,false> > debugFlags;
+GTSAM_EXPORT FastMap<std::string, ValueWithDefault<bool, false> > debugFlags;
+
+#ifdef GTSAM_USE_TBB
+tbb::mutex debugFlagsMutex;
+#endif
+
+/* ************************************************************************* */
+bool guardedIsDebug(const std::string& s) {
+#ifdef GTSAM_USE_TBB
+  tbb::mutex::scoped_lock lock(debugFlagsMutex);
+#endif
+  return gtsam::debugFlags[s];
+}
+
+/* ************************************************************************* */
+void guardedSetDebug(const std::string& s, const bool v) {
+#ifdef GTSAM_USE_TBB
+  tbb::mutex::scoped_lock lock(debugFlagsMutex);
+#endif
+  gtsam::debugFlags[s] = v;
+}
 
 }
diff --git a/gtsam/base/debug.h b/gtsam/base/debug.h
index f416bd826..f11245b1d 100644
--- a/gtsam/base/debug.h
+++ b/gtsam/base/debug.h
@@ -43,6 +43,10 @@
 
 namespace gtsam {
   GTSAM_EXTERN_EXPORT FastMap<std::string, ValueWithDefault<bool,false> > debugFlags;
+
+  // thread-safe functions to access debugFlags map
+  bool guardedIsDebug(const std::string& s);
+  void guardedSetDebug(const std::string& s, const bool v);
 }
 
 #undef ISDEBUG
@@ -50,8 +54,8 @@ namespace gtsam {
 
 #ifdef GTSAM_ENABLE_DEBUG
 
-#define ISDEBUG(S) (gtsam::debugFlags[S])
-#define SETDEBUG(S,V) ((void)(gtsam::debugFlags[S] = (V)))
+#define ISDEBUG(S) (gtsam::guardedIsDebug(S))
+#define SETDEBUG(S,V) ((void)(gtsam::guardedSetDebug(S,V)))
 
 #else