diff --git a/lib/Support/SlowOperationInformer.cpp b/lib/Support/SlowOperationInformer.cpp
index 40759f6d487..9dc2750f769 100644
--- a/lib/Support/SlowOperationInformer.cpp
+++ b/lib/Support/SlowOperationInformer.cpp
@@ -17,6 +17,7 @@
 #include <sstream>
 #include <signal.h>
 #include <unistd.h>
+#include <cassert>
 using namespace llvm;
 
 /// OperationCancelled - This flag is set by the SIGINT signal handler if the