diff --git a/lib/nghttp2_frame.c b/lib/nghttp2_frame.c
index 077ae1e6..c6318c1e 100644
--- a/lib/nghttp2_frame.c
+++ b/lib/nghttp2_frame.c
@@ -640,6 +640,8 @@ int nghttp2_iv_check(const nghttp2_settings_entry *iv, size_t niv)
         return 0;
       }
       break;
+    default:
+      return 0;
     }
   }
   return 1;
diff --git a/tests/nghttp2_frame_test.c b/tests/nghttp2_frame_test.c
index 56abc95d..d6495d19 100644
--- a/tests/nghttp2_frame_test.c
+++ b/tests/nghttp2_frame_test.c
@@ -434,4 +434,9 @@ void test_nghttp2_iv_check(void)
   CU_ASSERT(nghttp2_iv_check(iv, 2));
   iv[1].value = 3;
   CU_ASSERT(!nghttp2_iv_check(iv, 2));
+
+  /* Undefined SETTINGS ID */
+  iv[1].settings_id = 1000000009;
+  iv[1].value = 0;
+  CU_ASSERT(!nghttp2_iv_check(iv, 2));
 }