diff --git a/libc/bionic/pthread_sigmask.cpp b/libc/bionic/pthread_sigmask.cpp
new file mode 100644
index 0000000..9c9dc3e
--- /dev/null
+++ b/libc/bionic/pthread_sigmask.cpp
@@ -0,0 +1,62 @@
+/*
+ * 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 <pthread.h>
+#include <signal.h>
+
+#include <private/kernel_sigset_t.h>
+
+extern "C" int __rt_sigprocmask(int, const kernel_sigset_t*, kernel_sigset_t*, size_t);
+
+int pthread_sigmask(int how, const sigset_t* iset, sigset_t* oset) {
+  int old_errno = errno;
+
+  // 'in_set_ptr' is the second parameter to __rt_sigprocmask. It must be NULL
+  // if 'set' is NULL to ensure correct semantics (which in this case would
+  // be to ignore 'how' and return the current signal set into 'oset').
+  kernel_sigset_t in_set;
+  kernel_sigset_t* in_set_ptr = NULL;
+  if (iset != NULL) {
+    in_set.set(iset);
+    in_set_ptr = &in_set;
+  }
+
+  kernel_sigset_t out_set;
+  int result = __rt_sigprocmask(how, in_set_ptr, &out_set, sizeof(out_set));
+  if (result < 0) {
+    result = errno;
+  }
+
+  if (oset != NULL) {
+    *oset = out_set.bionic;
+  }
+
+  errno = old_errno;
+  return result;
+}