diff --git a/tests/sys_ioctl_diag_test.cpp b/tests/sys_ioctl_diag_test.cpp
new file mode 100644
index 0000000..e271e6c
--- /dev/null
+++ b/tests/sys_ioctl_diag_test.cpp
@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// This file makes uses of clang's built-in diagnostic checker.
+// While not officially supported by clang, it's used by clang for all of its
+// own diagnostic tests. Please see
+// https://clang.llvm.org/doxygen/classclang_1_1VerifyDiagnosticConsumer.html#details
+// for details.
+
+// expected-no-diagnostics
+
+#include <sys/ioctl.h>
+
+#pragma clang diagnostic warning "-Wsign-conversion"
+
+void check_no_signedness_warnings(int i, unsigned x) {
+  ioctl(i, i);
+  ioctl(i, x);
+
+  ioctl(i, i, nullptr);
+  ioctl(i, x, nullptr);
+}