diff --git a/src/getopt.h b/src/getopt.h
index 965dc29003..492c7911c5 100644
--- a/src/getopt.h
+++ b/src/getopt.h
@@ -6,6 +6,7 @@
 /* macros defined by this include file */
 #define no_argument       0
 #define required_argument 1
+#define optional_argument 2
 #define OPTIONAL_ARG      2
 
 /* types defined by this include file */