diff --git a/tools/flock/src/flock.c b/tools/flock/src/flock.c
index 13baec46ca4d5fdbfd496df6c90b0d0870d31c9b..3ac3a4bebce85225d4188149970ef94a74be6549 100644
--- a/tools/flock/src/flock.c
+++ b/tools/flock/src/flock.c
@@ -39,6 +39,7 @@
 #include <sys/file.h>
 #include <sys/time.h>
 #include <sys/wait.h>
+#include <fcntl.h>
 
 #define PACKAGE_STRING "util-linux-ng 2.18"
 #define _(x) (x)