diff --git a/flang/include/flang/Runtime/freestanding-tools.h b/flang/include/flang/Runtime/freestanding-tools.h
index 6753b7a24ebe1..7ef7cc74f213b 100644
--- a/flang/include/flang/Runtime/freestanding-tools.h
+++ b/flang/include/flang/Runtime/freestanding-tools.h
@@ -13,6 +13,7 @@
 #include "flang/Runtime/c-or-cpp.h"
 #include <algorithm>
 #include <cctype>
+#include <cstdlib>
 #include <cstring>
 
 // The file defines a set of utilities/classes that might be