diff --git a/unittests/Support/SignalsTest.cpp b/unittests/Support/SignalsTest.cpp
index 6dfa4bf996d..8c595c203ae 100644
--- a/unittests/Support/SignalsTest.cpp
+++ b/unittests/Support/SignalsTest.cpp
@@ -9,6 +9,7 @@
 #if !defined(_WIN32)
 #include <unistd.h>
 #include <sysexits.h>
+#include <signal.h>
 #endif // !defined(_WIN32)
 
 #include "llvm/Support/Signals.h"