diff --git a/mrbgems/mruby-method/src/method.c b/mrbgems/mruby-method/src/method.c
index bd49c94d2..77b29374f 100644
--- a/mrbgems/mruby-method/src/method.c
+++ b/mrbgems/mruby-method/src/method.c
@@ -410,16 +410,18 @@ method_to_s(mrb_state *mrb, mrb_value self)
     mrb_str_concat(mrb, str, name);
   }
  finish:;
-  const struct RProc *p = mrb_proc_ptr(proc);
-  if (MRB_PROC_ALIAS_P(p)) {
-    mrb_sym mid;
-    while (MRB_PROC_ALIAS_P(p)) {
-      mid = p->body.mid;
-      p = p->upper;
+  if (!mrb_nil_p(proc)) {
+    const struct RProc *p = mrb_proc_ptr(proc);
+    if (MRB_PROC_ALIAS_P(p)) {
+      mrb_sym mid;
+      while (MRB_PROC_ALIAS_P(p)) {
+        mid = p->body.mid;
+        p = p->upper;
+      }
+      mrb_str_cat_lit(mrb, str, "(");
+      mrb_str_concat(mrb, str, mrb_symbol_value(mid));
+      mrb_str_cat_lit(mrb, str, ")");
     }
-    mrb_str_cat_lit(mrb, str, "(");
-    mrb_str_concat(mrb, str, mrb_symbol_value(mid));
-    mrb_str_cat_lit(mrb, str, ")#");
   }
   mrb_value loc = method_source_location(mrb, self);
   if (mrb_array_p(loc) && RARRAY_LEN(loc) == 2) {