diff --git a/pidfilefn.c b/pidfilefn.c
index 2bbbdfb..b39bcce 100644
--- a/pidfilefn.c
+++ b/pidfilefn.c
@@ -19,6 +19,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <signal.h>
+#include <unistd.h>
 
 extern char *chomp(char *str);