diff --git a/libc/bionic/flockfile.cpp b/libc/bionic/flockfile.cpp
new file mode 100644
index 0000000..c60497d
--- /dev/null
+++ b/libc/bionic/flockfile.cpp
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2008 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <errno.h>
+#include <stdio.h>
+
+#include "fileext.h"
+
+// We can't use the OpenBSD implementation which uses kernel-specific
+// APIs not available on Linux. Instead we use a pthread_mutex_t within
+// struct __sfileext (see fileext.h).
+
+void flockfile(FILE* fp) {
+  if (fp != NULL) {
+    pthread_mutex_lock(&_FLOCK(fp));
+  }
+}
+
+int ftrylockfile(FILE* fp) {
+  // The specification for ftrylockfile() says it returns 0 on success,
+  // or non-zero on error. So return an errno code directly on error.
+  if (fp == NULL) {
+    return EINVAL;
+  }
+
+  return pthread_mutex_trylock(&_FLOCK(fp));
+}
+
+void funlockfile(FILE* fp) {
+  if (fp != NULL) {
+    pthread_mutex_unlock(&_FLOCK(fp));
+  }
+}