diff --git a/lib/getopt.c b/lib/getopt.c
index 0eb3a770..068ce519 100644
--- a/lib/getopt.c
+++ b/lib/getopt.c
@@ -84,6 +84,10 @@ int lib_getopt(int argc, char *const argv[], const char *optstring)
 			/* Argument in the same argv */
 			optarg = &argv[optind][getopt_common.optwhere];
 		}
+		else if (*(++optspec) == ':') {
+			/* Optional argument */
+			optarg = NULL;
+		}
 		else if (optind + 1 < argc) {
 			/* Argument in the next argv */
 			optarg = argv[optind + 1];