diff --git a/clients/roscpp/include/ros/timer.h b/clients/roscpp/include/ros/timer.h
index 2d5663e443..92f089cb23 100644
--- a/clients/roscpp/include/ros/timer.h
+++ b/clients/roscpp/include/ros/timer.h
@@ -71,7 +71,7 @@ class ROSCPP_DECL Timer
    */
   void setPeriod(const Duration& period, bool reset=true);
 
-  bool hasStarted() const { return impl_->hasStarted(); }
+  bool hasStarted() const { return impl_ && impl_->hasStarted(); }
   bool isValid() { return impl_ && impl_->isValid(); }
   operator void*() { return isValid() ? (void*)1 : (void*)0; }