diff --git a/polyp/xmalloc.c b/polyp/xmalloc.c
index 709e46e5e..981b3c924 100644
--- a/polyp/xmalloc.c
+++ b/polyp/xmalloc.c
@@ -26,6 +26,7 @@
 #include <stdlib.h>
 #include <signal.h>
 #include <assert.h>
+#include <unistd.h>
 
 #include "memory.h"
 #include "util.h"