diff --git a/mrbgems/mruby-sprintf/src/sprintf.c b/mrbgems/mruby-sprintf/src/sprintf.c
index d02a2aa4d..a3e20d83a 100644
--- a/mrbgems/mruby-sprintf/src/sprintf.c
+++ b/mrbgems/mruby-sprintf/src/sprintf.c
@@ -1087,6 +1087,9 @@ retry:
 
         CHECK(need);
         n = snprintf(&buf[blen], need, fbuf, fval);
+        if (n < 0) {
+          mrb_raise(mrb, E_RUNTIME_ERROR, "formatting error");
+        }
         blen += n;
       }
       break;