diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ui_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_ui --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ui.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUiTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ui(UINT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUiTest, ZeroHot) {
+  for (unsigned i = 0U; i != UINT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ui(~(1U << i)),
+              UINT_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ul_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_ul --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ul.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUlTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ul(ULONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUlTest, ZeroHot) {
+  for (unsigned i = 0U; i != ULONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ul(~(1UL << i)),
+              ULONG_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_ull_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_ull -------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_ull.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUllTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ull(ULLONG_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUllTest, ZeroHot) {
+  for (unsigned i = 0U; i != ULLONG_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_ull(~(1ULL << i)),
+              ULLONG_WIDTH - i);
+}
diff --git a/libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp b/libc/test/src/stdbit/stdc_first_leading_zero_us_test.cpp
@@ -0,0 +1,21 @@
+//===-- Unittests for stdc_first_leading_zero_us --------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/__support/CPP/limits.h"
+#include "src/stdbit/stdc_first_leading_zero_us.h"
+#include "test/UnitTest/Test.h"
+
+TEST(LlvmLibcStdcFirstLeadingZeroUsTest, ALL) {
+  EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_us(USHRT_MAX), 0U);
+}
+
+TEST(LlvmLibcStdcFirstLeadingZeroUsTest, ZeroHot) {
+  for (unsigned i = 0U; i != USHRT_WIDTH; ++i)
+    EXPECT_EQ(LIBC_NAMESPACE::stdc_first_leading_zero_us(~(1U << i)),
+              USHRT_WIDTH - i);
+}