diff --git a/string.c b/string.c
index dee17c86a6..0b3878b9b1 100644
--- a/string.c
+++ b/string.c
@@ -3763,9 +3763,7 @@ rb_str_append_as_bytes(int argc, VALUE *argv, VALUE str)
             break;
           }
           default:
-            UNREACHABLE;
-            RUBY_ASSERT("append_as_bytes arguments should have been validated");
-            break;
+            rb_bug("append_as_bytes arguments should have been validated");
         }
     }
 
@@ -3793,9 +3791,7 @@ rb_str_append_as_bytes(int argc, VALUE *argv, VALUE str)
                 break;
               }
               default:
-                UNREACHABLE;
-                RUBY_ASSERT("append_as_bytes arguments should have been validated");
-                break;
+                rb_bug("append_as_bytes arguments should have been validated");
             }
         }
         break;