diff --git a/libc/umask.cpp b/libc/umask.cpp
index d62e99e1..bf043f59 100644
--- a/libc/umask.cpp
+++ b/libc/umask.cpp
@@ -1,6 +1,6 @@
 /*******************************************************************************
 
-    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012.
+    Copyright(C) Jonas 'Sortie' Termansen 2013.
 
     This file is part of the Sortix C Library.
 
@@ -24,12 +24,10 @@
 
 #include <sys/stat.h>
 #include <sys/syscall.h>
-#include <sys/types.h>
-#include <errno.h>
 
-// TODO: Implement this in the kernel.
+DEFN_SYSCALL1(mode_t, sys_umask, SYSCALL_UMASK, mode_t);
+
 extern "C" mode_t umask(mode_t mask)
 {
-	(void) mask;
-	return 0;
+	return sys_umask(mask);
 }
diff --git a/sortix/descriptor.cpp b/sortix/descriptor.cpp
index ca1a4f33..08ed411f 100644
--- a/sortix/descriptor.cpp
+++ b/sortix/descriptor.cpp
@@ -356,6 +356,11 @@ static bool IsLastPathElement(const char* elem)
 Ref<Descriptor> Descriptor::open(ioctx_t* ctx, const char* filename, int flags,
                                  mode_t mode)
 {
+	Process* process = CurrentProcess();
+	kthread_mutex_lock(&process->idlock);
+	mode &= ~process->umask;
+	kthread_mutex_unlock(&process->idlock);
+
 	// Unlike early Unix systems, the empty path does not mean the current
 	// directory on Sortix, so reject it.
 	if ( !filename[0] )
@@ -444,6 +449,11 @@ Ref<Descriptor> Descriptor::open_elem(ioctx_t* ctx, const char* filename,
 
 int Descriptor::mkdir(ioctx_t* ctx, const char* filename, mode_t mode)
 {
+	Process* process = CurrentProcess();
+	kthread_mutex_lock(&process->idlock);
+	mode &= ~process->umask;
+	kthread_mutex_unlock(&process->idlock);
+
 	char* final;
 	Ref<Descriptor> dir = OpenDirContainingPath(ctx, Ref<Descriptor>(this),
 	                                            filename, &final);
diff --git a/sortix/include/sortix/kernel/process.h b/sortix/include/sortix/kernel/process.h
index d74ba467..276a22a7 100644
--- a/sortix/include/sortix/kernel/process.h
+++ b/sortix/include/sortix/kernel/process.h
@@ -96,6 +96,7 @@ public:
 	kthread_mutex_t idlock;
 	uid_t uid, euid;
 	gid_t gid, egid;
+	mode_t umask;
 
 private:
 	kthread_mutex_t ptrlock;
diff --git a/sortix/include/sortix/syscallnum.h b/sortix/include/sortix/syscallnum.h
index 664abe06..da74eb5e 100644
--- a/sortix/include/sortix/syscallnum.h
+++ b/sortix/include/sortix/syscallnum.h
@@ -128,6 +128,7 @@
 #define SYSCALL_CLOCK_SETTIMERES 104
 #define SYSCALL_CLOCK_NANOSLEEP 105
 #define SYSCALL_TIMENS 106
-#define SYSCALL_MAX_NUM 107 /* index of highest constant + 1 */
+#define SYSCALL_UMASK 107
+#define SYSCALL_MAX_NUM 108 /* index of highest constant + 1 */
 
 #endif
diff --git a/sortix/process.cpp b/sortix/process.cpp
index 84b67bd6..b4c9d2e2 100644
--- a/sortix/process.cpp
+++ b/sortix/process.cpp
@@ -131,6 +131,7 @@ namespace Sortix
 		pid = AllocatePID();
 		uid = euid = 0;
 		gid = egid = 0;
+		umask = 0022;
 		Time::InitializeProcessClocks(this);
 		alarm_timer.Attach(Time::GetClock(CLOCK_MONOTONIC));
 		Put(this);
@@ -611,6 +612,7 @@ namespace Sortix
 		clone->gid = gid;
 		clone->euid = euid;
 		clone->egid = egid;
+		clone->umask = umask;
 		kthread_mutex_unlock(&idlock);
 
 		if ( !(clone->program_image_path = String::Clone(program_image_path)) )
@@ -978,6 +980,15 @@ namespace Sortix
 		return Page::Size();
 	}
 
+	mode_t sys_umask(mode_t newmask)
+	{
+		Process* process = CurrentProcess();
+		ScopedLock lock(&process->idlock);
+		mode_t oldmask = process->umask;
+		process->umask = newmask & 0666;
+		return oldmask;
+	}
+
 	void Process::Init()
 	{
 		Syscall::Register(SYSCALL_EXEC, (void*) SysExecVE);
@@ -985,6 +996,7 @@ namespace Sortix
 		Syscall::Register(SYSCALL_GETPID, (void*) SysGetPID);
 		Syscall::Register(SYSCALL_GETPPID, (void*) SysGetParentPID);
 		Syscall::Register(SYSCALL_EXIT, (void*) SysExit);
+		Syscall::Register(SYSCALL_UMASK, (void*) sys_umask);
 		Syscall::Register(SYSCALL_WAIT, (void*) SysWait);
 		Syscall::Register(SYSCALL_SBRK, (void*) SysSbrk);
 		Syscall::Register(SYSCALL_GET_PAGE_SIZE, (void*) SysGetPageSize);
diff --git a/utils/init.cpp b/utils/init.cpp
index 9a1f5556..6595766f 100644
--- a/utils/init.cpp
+++ b/utils/init.cpp
@@ -1,6 +1,6 @@
 /*******************************************************************************
 
-    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012.
+    Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013.
 
     This program is free software: you can redistribute it and/or modify it
     under the terms of the GNU General Public License as published by the Free
@@ -75,6 +75,9 @@ int main(int /*argc*/, char* /*argv*/[])
 	printf("\r\e[m\e[J");
 	fflush(stdout);
 
+	// Set the default file creation mask.
+	umask(022);
+
 	// By default, compile to the same architecture that the kernel told us that
 	// we are running.
 	setenv("objtype", getenv("cputype"), 0);