diff --git a/tests/Android.bp b/tests/Android.bp
index ec90296..eb3b5f4 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -48,6 +48,18 @@
 // All standard tests.
 // -----------------------------------------------------------------------------
 
+// Test diagnostics emitted by clang. The library that results is useless; we
+// just want to run '-Xclang -verify', which will fail if the diagnostics don't
+// match up with what the source file says they should be.
+cc_test_library {
+    name: "clang_diagnostic_tests",
+    cflags: [
+      "-Xclang",
+      "-verify",
+    ],
+    srcs: ["sys_ioctl_diag_test.cpp"],
+}
+
 cc_test_library {
     name: "libBionicStandardTests",
     defaults: ["bionic_tests_defaults"],
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);
+}