diff --git a/dtool/src/dtoolbase/memoryHook.cxx b/dtool/src/dtoolbase/memoryHook.cxx
index f944c22e89..c11dde4f34 100644
--- a/dtool/src/dtoolbase/memoryHook.cxx
+++ b/dtool/src/dtoolbase/memoryHook.cxx
@@ -18,6 +18,7 @@
 
 #include "memoryHook.h"
 #include "deletedBufferChain.h"
+#include <stdlib.h>
 
 #ifdef WIN32