diff --git a/param.c b/param.c
index e24757a..ceb7f48 100644
--- a/param.c
+++ b/param.c
@@ -109,7 +109,7 @@ Param_Tweak(struct ocx *ocx, const char *arg)
 			if (!strcmp(pt->name, arg))
 				break;
 		if (pt == NULL)
-			Fail(ocx, 0, "unknown parameter '%s' (try PARAM ?)",
+			Fail(ocx, 0, "unknown parameter '%s' (try PARAM=?)",
 			    arg);
 		Put(ocx, OCX_DIAG, "Parameter:\n\t%s\n", pt->name);
 		Put(ocx, OCX_DIAG, "Minimum:\n\t%.3e\n", pt->min);
@@ -131,7 +131,7 @@ Param_Tweak(struct ocx *ocx, const char *arg)
 			break;
 	}
 	if (pt == NULL)
-		Fail(ocx, 0, "unknown parameter '%.*s' (try PARAM ?)",
+		Fail(ocx, 0, "unknown parameter '%.*s' (try PARAM=?)",
 		    (int)(q - arg), arg);
 
 	r = NULL;