diff --git a/libc/include/signal.h b/libc/include/signal.h
index 3b7efd2e..eb70a84c 100644
--- a/libc/include/signal.h
+++ b/libc/include/signal.h
@@ -207,7 +207,7 @@ int killpg(pid_t, int);
 void psiginfo(const siginfo_t*, const char*);
 void psignal(int, const char*);
 /* TODO: int pthread_kill(pthread_t, int); */
-/* TODO: int pthread_sigmask(int, const sigset_t* __restrict, sigset_t* __restrict); */
+int pthread_sigmask(int, const sigset_t* __restrict, sigset_t* __restrict);
 int raise(int sig);
 int sigaction(int, const struct sigaction* __restrict, struct sigaction* __restrict);
 int sigaddset(sigset_t*, int);
diff --git a/libpthread/Makefile b/libpthread/Makefile
index 2f63fe21..aaa209ac 100644
--- a/libpthread/Makefile
+++ b/libpthread/Makefile
@@ -46,6 +46,7 @@ pthread_rwlock_unlock.o \
 pthread_rwlock_wrlock.o \
 pthread_self.o \
 pthread_setspecific.o \
+pthread_sigmask.o \
 
 BINS:=libpthread.a
 
diff --git a/libpthread/pthread_sigmask.c++ b/libpthread/pthread_sigmask.c++
new file mode 100644
index 00000000..e5fdb44e
--- /dev/null
+++ b/libpthread/pthread_sigmask.c++
@@ -0,0 +1,35 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2014.
+
+    This file is part of Sortix libpthread.
+
+    Sortix libpthread is free software: you can redistribute it and/or modify it
+    under the terms of the GNU Lesser General Public License as published by the
+    Free Software Foundation, either version 3 of the License, or (at your
+    option) any later version.
+
+    Sortix libpthread is distributed in the hope that it will be useful, but
+    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+    or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
+    License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with Sortix libpthread. If not, see <http://www.gnu.org/licenses/>.
+
+    pthread_sigmask.c++
+    Examine and change blocked signals.
+
+*******************************************************************************/
+
+#include <errno.h>
+#include <signal.h>
+#include <pthread.h>
+
+extern "C"
+int pthread_sigmask(int how,
+                    const sigset_t* restrict set,
+                    sigset_t* restrict oldset)
+{
+	return sigprocmask(how, set, oldset) < 0 ? errno : 0;
+}