diff --git a/scripts/headerdep.pl b/scripts/headerdep.pl
index 97399da..b7f6c56 100755
--- a/scripts/headerdep.pl
+++ b/scripts/headerdep.pl
@@ -19,7 +19,7 @@
 	version	=> \&version,
 
 	all	=> \$opt_all,
-	I	=> \@opt_include,
+	"I=s"	=> \@opt_include,
 	graph	=> \$opt_graph,
 );