diff --git a/tools/headerversions.c b/tools/headerversions.c
index 8adf4ef35..0dde4efad 100644
--- a/tools/headerversions.c
+++ b/tools/headerversions.c
@@ -10,6 +10,7 @@
 #include <sqlite3.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <unistd.h>
 #include <zlib.h>
 
 static const char template[] =