diff --git a/util/stdlib/strnlen.cc b/util/stdlib/strnlen.cc
new file mode 100644
index 00000000..b17796bb
--- /dev/null
+++ b/util/stdlib/strnlen.cc
@@ -0,0 +1,37 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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.
+
+#include "util/stdlib/strnlen.h"
+
+namespace crashpad {
+
+#if defined(OS_MACOSX) && MAC_OS_X_VERSION_MIN_REQUIRED < MAC_OS_X_VERSION_10_7
+size_t strnlen(const char* string, size_t max_length) {
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_7
+  if (::strnlen) {
+    return ::strnlen(string, max_length);
+  }
+#endif
+
+  for (size_t index = 0; index < max_length; ++index) {
+    if (string[index] == '\0') {
+      return index;
+    }
+  }
+
+  return max_length;
+}
+#endif
+
+}  // namespace crashpad
diff --git a/util/stdlib/strnlen.h b/util/stdlib/strnlen.h
new file mode 100644
index 00000000..f1bbe638
--- /dev/null
+++ b/util/stdlib/strnlen.h
@@ -0,0 +1,49 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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.
+
+#ifndef CRASHPAD_UTIL_STDLIB_STRNLEN_H_
+#define CRASHPAD_UTIL_STDLIB_STRNLEN_H_
+
+#include <string.h>
+
+#include "build/build_config.h"
+
+#if defined(OS_MACOSX)
+#include <AvailabilityMacros.h>
+#endif
+
+namespace crashpad {
+
+//! \brief Returns the length of a string, not to exceed a maximum.
+//!
+//! \param[in] string The string whose length is to be calculated.
+//! \param[in] max_length The maximum length to return.
+//!
+//! \return The length of \a string, determined as the index of the first `NUL`
+//!     byte found, not exceeding \a max_length.
+//!
+//! \note This function is provided because it was introduced in POSIX.1-2008,
+//!     and not all systems’ standard libraries provide an implementation.
+size_t strnlen(const char* string, size_t max_length);
+
+#if !defined(OS_MACOSX) || \
+    MAC_OS_X_VERSION_MIN_REQUIRED >= MAC_OS_X_VERSION_10_7
+inline size_t strnlen(const char* string, size_t max_length) {
+  return ::strnlen(string, max_length);
+}
+#endif
+
+}  // namespace crashpad
+
+#endif  // CRASHPAD_UTIL_STDLIB_STRNLEN_H_
diff --git a/util/stdlib/strnlen_test.cc b/util/stdlib/strnlen_test.cc
new file mode 100644
index 00000000..f5b6845b
--- /dev/null
+++ b/util/stdlib/strnlen_test.cc
@@ -0,0 +1,41 @@
+// Copyright 2014 The Crashpad Authors. All rights reserved.
+//
+// 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.
+
+#include "util/stdlib/strnlen.h"
+
+#include <string.h>
+
+#include "gtest/gtest.h"
+
+namespace {
+
+TEST(strnlen, strnlen) {
+  const char kTestBuffer[] = "abc\0d";
+  ASSERT_EQ(3u, strlen(kTestBuffer));
+  EXPECT_EQ(0u, crashpad::strnlen(kTestBuffer, 0));
+  EXPECT_EQ(1u, crashpad::strnlen(kTestBuffer, 1));
+  EXPECT_EQ(2u, crashpad::strnlen(kTestBuffer, 2));
+  EXPECT_EQ(3u, crashpad::strnlen(kTestBuffer, 3));
+  EXPECT_EQ(3u, crashpad::strnlen(kTestBuffer, 4));
+  EXPECT_EQ(3u, crashpad::strnlen(kTestBuffer, 5));
+  EXPECT_EQ(3u, crashpad::strnlen(kTestBuffer, 6));
+
+  const char kEmptyBuffer[] = "\0";
+  ASSERT_EQ(0u, strlen(kEmptyBuffer));
+  EXPECT_EQ(0u, crashpad::strnlen(kEmptyBuffer, 0));
+  EXPECT_EQ(0u, crashpad::strnlen(kEmptyBuffer, 1));
+  EXPECT_EQ(0u, crashpad::strnlen(kEmptyBuffer, 2));
+}
+
+}  // namespace
diff --git a/util/util.gyp b/util/util.gyp
index 4a6c56e7..7af42568 100644
--- a/util/util.gyp
+++ b/util/util.gyp
@@ -74,6 +74,8 @@
         'stdlib/pointer_container.h',
         'stdlib/strlcpy.cc',
         'stdlib/strlcpy.h',
+        'stdlib/strnlen.cc',
+        'stdlib/strnlen.h',
       ],
     },
     {
@@ -136,6 +138,7 @@
         'numeric/in_range_cast_test.cc',
         'posix/process_util_test.cc',
         'stdlib/strlcpy_test.cc',
+        'stdlib/strnlen_test.cc',
         'test/mac/mach_multiprocess_test.cc',
         'test/multiprocess_test.cc',
       ],