diff --git a/lib/if.c b/lib/if.c
index 43e84a4..8fbaa76 100644
--- a/lib/if.c
+++ b/lib/if.c
@@ -203,7 +203,7 @@
       if (ifp->ifindex == index)
 	return ifp->name;
     }
-  return "unknown";
+  return (char *) "unknown";
 }
 
 /* Interface existance check by interface name. */