diff --git a/libc/Makefile b/libc/Makefile
index 0f2775b5..ece8baa4 100644
--- a/libc/Makefile
+++ b/libc/Makefile
@@ -92,6 +92,11 @@ op-new.o \
 rewind.o \
 setbuf.o \
 setvbuf.o \
+sigaddset.o \
+sigdelset.o \
+sigfillset.o \
+sigemptyset.o \
+sigismember.o \
 sort.o \
 sprint.o \
 sscanf.o \
diff --git a/libc/sigaddset.cpp b/libc/sigaddset.cpp
new file mode 100644
index 00000000..8005fd88
--- /dev/null
+++ b/libc/sigaddset.cpp
@@ -0,0 +1,39 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library 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.
+
+    The Sortix C Library 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 the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sigaddset.cpp
+    Add a signal to a signal set.
+
+*******************************************************************************/
+
+#include <errno.h>
+#include <signal.h>
+#include <stdint.h>
+
+extern "C" int sigaddset(sigset_t* set, int signum)
+{
+	int max_signals = sizeof(set->__val) * 8;
+	if ( max_signals <= signum )
+		return errno = EINVAL, -1;
+	size_t which_byte = signum / 8;
+	size_t which_bit  = signum % 8;
+	uint8_t* bytes = (uint8_t*) set->__val;
+	bytes[which_byte] |= 1 << which_bit;
+	return 0;
+}
diff --git a/libc/sigdelset.cpp b/libc/sigdelset.cpp
new file mode 100644
index 00000000..d614b8b3
--- /dev/null
+++ b/libc/sigdelset.cpp
@@ -0,0 +1,39 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library 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.
+
+    The Sortix C Library 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 the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sigdelset.cpp
+    Remove a signal from a signal set.
+
+*******************************************************************************/
+
+#include <errno.h>
+#include <signal.h>
+#include <stdint.h>
+
+extern "C" int sigdelset(sigset_t* set, int signum)
+{
+	int max_signals = sizeof(set->__val) * 8;
+	if ( max_signals <= signum )
+		return errno = EINVAL, -1;
+	size_t which_byte = signum / 8;
+	size_t which_bit  = signum % 8;
+	uint8_t* bytes = (uint8_t*) set->__val;
+	bytes[which_byte] &= ~(1 << which_bit);
+	return 0;
+}
diff --git a/libc/sigemptyset.cpp b/libc/sigemptyset.cpp
new file mode 100644
index 00000000..74df4c61
--- /dev/null
+++ b/libc/sigemptyset.cpp
@@ -0,0 +1,32 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library 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.
+
+    The Sortix C Library 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 the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sigemptyset.cpp
+    Removes all the signals from a signal set.
+
+*******************************************************************************/
+
+#include <signal.h>
+#include <string.h>
+
+extern "C" int sigemptyset(sigset_t* set)
+{
+	memset(set, 0, sizeof(*set));
+	return 0;
+}
diff --git a/libc/sigfillset.cpp b/libc/sigfillset.cpp
new file mode 100644
index 00000000..72261d64
--- /dev/null
+++ b/libc/sigfillset.cpp
@@ -0,0 +1,32 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library 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.
+
+    The Sortix C Library 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 the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sigfillset.cpp
+    Add all signals to a signal set.
+
+*******************************************************************************/
+
+#include <signal.h>
+#include <string.h>
+
+extern "C" int sigfillset(sigset_t* set)
+{
+	memset(set, 255, sizeof(*set));
+	return 0;
+}
diff --git a/libc/sigismember.cpp b/libc/sigismember.cpp
new file mode 100644
index 00000000..9900743b
--- /dev/null
+++ b/libc/sigismember.cpp
@@ -0,0 +1,38 @@
+/*******************************************************************************
+
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
+
+    This file is part of the Sortix C Library.
+
+    The Sortix C Library 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.
+
+    The Sortix C Library 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 the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
+
+    sigismember.cpp
+    Test signal membership in a signal set.
+
+*******************************************************************************/
+
+#include <errno.h>
+#include <signal.h>
+#include <stdint.h>
+
+extern "C" int sigismember(const sigset_t* set, int signum)
+{
+	int max_signals = sizeof(set->__val) * 8;
+	if ( max_signals <= signum )
+		return errno = EINVAL, -1;
+	size_t which_byte = signum / 8;
+	size_t which_bit  = signum % 8;
+	const uint8_t* bytes = (const uint8_t*) set->__val;
+	return bytes[which_byte] & (1 << which_bit) ? 1 : 0;
+}
diff --git a/libc/signal.cpp b/libc/signal.cpp
index 054913d9..a073af56 100644
--- a/libc/signal.cpp
+++ b/libc/signal.cpp
@@ -24,6 +24,7 @@
 
 #include <sys/types.h>
 #include <sys/syscall.h>
+
 #include <signal.h>
 
 const int MAX_SIGNALS = 128;