diff --git a/error.c b/error.c
index 97f8c22102..c01e887dd2 100644
--- a/error.c
+++ b/error.c
@@ -1271,8 +1271,7 @@ exc_full_message(int argc, VALUE *argv, VALUE exc)
 	rb_get_kwargs(opt, kw, 0, kw_max_, args);
 	switch (args[kw_highlight]) {
 	  default:
-	    rb_raise(rb_eArgError, "expected true or false as "
-		     "highlight: %+"PRIsVALUE, args[kw_highlight]);
+            rb_bool_expected(args[kw_highlight], "highlight");
 	  case Qundef: args[kw_highlight] = Qnil; break;
 	  case Qtrue: case Qfalse: case Qnil: break;
 	}
diff --git a/object.c b/object.c
index 350cef0aeb..4667c18822 100644
--- a/object.c
+++ b/object.c
@@ -3388,7 +3388,7 @@ rb_bool_expected(VALUE obj, const char *flagname)
       case Qtrue: case Qfalse:
         break;
       default:
-        rb_raise(rb_eArgError, "true or false is expected as %s: %+"PRIsVALUE,
+        rb_raise(rb_eArgError, "expected true or false as %s: %+"PRIsVALUE,
                  flagname, obj);
     }
     return obj != Qfalse;