diff --git a/conts/posix/mm0/mm/clone.c b/conts/posix/mm0/mm/clone.c
index 61b001f..eec8453 100644
--- a/conts/posix/mm0/mm/clone.c
+++ b/conts/posix/mm0/mm/clone.c
@@ -22,11 +22,6 @@ int sys_fork(struct tcb *parent)
 	struct tcb *child;
 	struct exregs_data exregs;
 	struct task_ids ids;
-//	 	= {
-//		.tid = TASK_ID_INVALID,
-//		.spid = parent->spid,		/* spid to copy from */
-//		.tgid = TASK_ID_INVALID,	/* FIXME: !!! FIX THIS */
-//	};
 
 	/* Make all shadows in this task read-only */
 	vm_freeze_shadows(parent);
@@ -36,8 +31,8 @@ int sys_fork(struct tcb *parent)
 	 * kernel stack and kernel-side tcb copied
 	 */
 	if (IS_ERR(child = task_create(parent, &ids,
-				       THREAD_COPY_SPACE,
-			    	       TCB_NO_SHARING)))
+			    	       TCB_NO_SHARING,
+				       TC_COPY_SPACE)))
 		return (int)child;
 
 	/* Set child's fork return value to 0 */
@@ -64,27 +59,17 @@ int sys_fork(struct tcb *parent)
 	return child->tid;
 }
 
-int do_clone(struct tcb *parent,
-	     unsigned long child_stack,
-	     unsigned int flags)
+int do_clone(struct tcb *parent, unsigned long child_stack,
+	     unsigned int flags, unsigned int sysflags)
 {
 	struct exregs_data exregs;
 	struct task_ids ids;
 	struct tcb *child;
 	int err;
 
-	/*
-	 * Determine whether the cloned
-	 * thread is in parent's thread group
-	 */
-	if (flags & TCB_SHARED_TGROUP)
-		ids.tgid = parent->tgid;
-	else
-		ids.tgid = TASK_ID_INVALID;
-
 	if (IS_ERR(child = task_create(parent, &ids,
-				       THREAD_SAME_SPACE,
-				       flags)))
+				       flags,
+				       sysflags)))
 		return (int)child;
 
 	/* Set up child stack marks with given stack argument */
@@ -122,23 +107,28 @@ int sys_clone(struct tcb *parent,
 	      unsigned int clone_flags)
 {
 	unsigned int flags = 0;
+	unsigned int sysflags = 0;
 
 	if (!child_stack)
 		return -EINVAL;
 
-	if (clone_flags & CLONE_VM)
+	if (clone_flags & CLONE_VM) {
 		flags |= TCB_SHARED_VM;
+		sysflags |= TC_SHARE_SPACE;
+	}
 	if (clone_flags & CLONE_FS)
 		flags |= TCB_SHARED_FS;
 	if (clone_flags & CLONE_FILES)
 		flags |= TCB_SHARED_FILES;
-	if (clone_flags & CLONE_THREAD)
+	if (clone_flags & CLONE_THREAD) {
 		flags |= TCB_SHARED_TGROUP;
+		sysflags |= TC_SHARE_GROUP;
+	}
 	if (clone_flags & CLONE_PARENT)
 		flags |= TCB_SHARED_PARENT;
 
 	return do_clone(parent,
 			(unsigned long)child_stack,
-			flags);
+			flags, sysflags);
 }
 
diff --git a/conts/posix/mm0/mm/execve.c b/conts/posix/mm0/mm/execve.c
index 5da170d..93dcd99 100644
--- a/conts/posix/mm0/mm/execve.c
+++ b/conts/posix/mm0/mm/execve.c
@@ -79,8 +79,8 @@ int init_execve(char *filepath)
 	vmfile = self->files->fd[fd].vmfile;
 
 	if (IS_ERR(new_task = task_create(0, &ids,
-					  THREAD_NEW_SPACE,
-					  TCB_NO_SHARING))) {
+					  TCB_NO_SHARING,
+					  TC_NEW_SPACE))) {
 		sys_close(self, fd);
 		return (int)new_task;
 	}
diff --git a/conts/posix/mm0/mm/task.c b/conts/posix/mm0/mm/task.c
index 4255e84..29e8342 100644
--- a/conts/posix/mm0/mm/task.c
+++ b/conts/posix/mm0/mm/task.c
@@ -342,7 +342,7 @@ int copy_tcb(struct tcb *to, struct tcb *from, unsigned int share_flags)
 }
 
 struct tcb *task_create(struct tcb *parent, struct task_ids *ids,
-			unsigned int ctrl_flags, unsigned int share_flags)
+			unsigned int share_flags, unsigned int ctrl_flags)
 {
 	struct tcb *task;
 	int err;
@@ -354,15 +354,7 @@ struct tcb *task_create(struct tcb *parent, struct task_ids *ids,
 	if (parent) {
 		ids->tid = parent->tid;
 		ids->spid = parent->spid;
-
-		/*
-		 * Determine whether the cloned thread
-		 * is in parent's thread group
-		 */
-		if (share_flags & TCB_SHARED_TGROUP)
-			ids->tgid = parent->tgid;
-		else
-			ids->tgid = TASK_ID_INVALID;
+		ids->tgid = parent->tgid;
 	}
 
 	/* Create the thread structures and address space */
diff --git a/include/l4/api/thread.h b/include/l4/api/thread.h
index 0c5eb45..f885abc 100644
--- a/include/l4/api/thread.h
+++ b/include/l4/api/thread.h
@@ -1,30 +1,21 @@
 #ifndef __THREAD_H__
 #define __THREAD_H__
 
-#define THREAD_CREATE_MASK		0x0030
+#define THREAD_ACTION_MASK	0x000F
+#define THREAD_CREATE		0x0000
+#define THREAD_RUN		0x0001
+#define THREAD_SUSPEND		0x0002
+#define THREAD_RESUME		0x0003
+#define THREAD_DESTROY		0x0004
+#define THREAD_RECYCLE		0x0005
 
-/* Create new thread and new space */
-#define THREAD_NEW_SPACE		0x0010
-
-/* Create new thread, copy given space */
-#define THREAD_COPY_SPACE		0x0020
-
-/* Create new thread, use given space */
-#define THREAD_SAME_SPACE		0x0030
-
-/* Shared UTCB, New UTCB, No UTCB */
-#define THREAD_UTCB_MASK		0x00C0
-#define THREAD_UTCB_NEW			0x0040
-#define THREAD_UTCB_SAME		0x0080
-#define THREAD_UTCB_NONE		0x00C0
-
-
-#define THREAD_ACTION_MASK		0x000F
-#define THREAD_CREATE			0x0000
-#define THREAD_RUN			0x0001
-#define THREAD_SUSPEND			0x0002
-#define THREAD_RESUME			0x0003
-#define THREAD_DESTROY			0x0004
-#define THREAD_RECYCLE			0x0005
+#define THREAD_CREATE_MASK	0x03F0
+#define TC_SHARE_CAPS		0x0010	/* Share all thread capabilities */
+#define TC_SHARE_UTCB		0x0020	/* Share utcb location (same space */
+#define TC_SHARE_GROUP		0x0040	/* Share thread group id */
+#define TC_SHARE_SPACE		0x0080	/* New thread, use given space */
+#define TC_COPY_SPACE		0x0100	/* New thread, copy given space */
+#define TC_NEW_SPACE		0x0200	/* New thread, new space */
+#define TC_SHARE_PAGER		0x0400  /* New thread, shared pager */
 
 #endif /* __THREAD_H__ */
diff --git a/src/api/thread.c b/src/api/thread.c
index 24c28ab..c84956b 100644
--- a/src/api/thread.c
+++ b/src/api/thread.c
@@ -242,19 +242,19 @@ int arch_setup_new_thread(struct ktcb *new, struct ktcb *orig,
 			  unsigned int flags)
 {
 	/* New threads just need their mode set up */
-	if ((flags & THREAD_CREATE_MASK) == THREAD_NEW_SPACE) {
+	if (flags & TC_NEW_SPACE) {
 		BUG_ON(orig);
 		new->context.spsr = ARM_MODE_USR;
 		return 0;
 	}
 
+	BUG_ON(!orig);
 	/*
 	 * For duplicated threads pre-syscall context is saved on
 	 * the kernel stack. We copy this context of original
 	 * into the duplicate thread's current context structure
 	 *
-	 * We don't lock for context modification because the
-	 * thread is not known to the system yet.
+	 * No locks needed as the thread is not known to the system yet.
 	 */
 	BUG_ON(!(new->context.spsr = orig->syscall_regs->spsr)); /* User mode */
 	new->context.r0 = orig->syscall_regs->r0;
@@ -281,37 +281,18 @@ int arch_setup_new_thread(struct ktcb *new, struct ktcb *orig,
 	return 0;
 }
 
-/*
- * Sets up the thread, thread group and space id of newly created thread
- * according to supplied flags.
- */
-int thread_setup_new_ids(struct task_ids *ids, unsigned int flags,
-			 struct ktcb *new, struct ktcb *orig)
+static inline void
+thread_setup_new_ids(struct task_ids *ids, unsigned int flags,
+		     struct ktcb *new, struct ktcb *orig)
 {
+	if (flags & TC_SHARE_GROUP)
+		new->tgid = orig->tgid;
+	else
+		new->tgid = new->tid;
+
+	/* Update ids to be returned back to caller */
 	ids->tid = new->tid;
-
-	/*
-	 * If thread space is new or copied,
-	 * thread gets same group id as its thread id
-	 */
-	if (flags == THREAD_NEW_SPACE ||
-	    flags == THREAD_COPY_SPACE) {
-		ids->tgid = ids->tid;
-		new->tgid = new->tid;
-	}
-
-	/*
-	 * If the tgid of original thread is supplied, that implies the
-	 * new thread wants to be in the same group, and we leave it as
-	 * it is. Otherwise the thread gets the same group id as its
-	 * unique thread id.
-	 */
-	if (flags == THREAD_SAME_SPACE && ids->tgid != orig->tgid) {
-		ids->tgid = ids->tid;
-		new->tgid = new->tid;
-	}
-
-	return 0;
+	ids->tgid = new->tgid;
 }
 
 int thread_setup_space(struct ktcb *tcb, struct task_ids *ids, unsigned int flags)
@@ -321,14 +302,14 @@ int thread_setup_space(struct ktcb *tcb, struct task_ids *ids, unsigned int flag
 
 	address_space_reference_lock();
 
-	if (flags == THREAD_SAME_SPACE) {
+	if (flags & TC_SHARE_SPACE) {
 		if (!(space = address_space_find(ids->spid))) {
 			ret = -ESRCH;
 			goto out;
 		}
 		address_space_attach(tcb, space);
 	}
-	if (flags == THREAD_COPY_SPACE) {
+	if (flags & TC_COPY_SPACE) {
 		if (!(space = address_space_find(ids->spid))) {
 			ret = -ESRCH;
 			goto out;
@@ -342,7 +323,7 @@ int thread_setup_space(struct ktcb *tcb, struct task_ids *ids, unsigned int flag
 		address_space_attach(tcb, new);
 		address_space_add(new);
 	}
-	if (flags == THREAD_NEW_SPACE) {
+	if (flags & TC_NEW_SPACE) {
 		if (IS_ERR(new = address_space_create(0))) {
 			ret = (int)new;
 			goto out;
@@ -364,8 +345,22 @@ int thread_create(struct task_ids *ids, unsigned int flags)
 	struct ktcb *parent = 0;
 	int err;
 
+	/* Clear flags to just include creation flags */
 	flags &= THREAD_CREATE_MASK;
 
+	/* Can't have multiple space directives in flags */
+	if ((flags & TC_SHARE_SPACE & TC_COPY_SPACE & TC_NEW_SPACE)
+	    || !flags)
+		return -EINVAL;
+
+	/* Can't request shared utcb or tgid without shared space */
+	if (!(flags & TC_SHARE_SPACE)) {
+		if ((flags & TC_SHARE_UTCB) ||
+		    (flags & TC_SHARE_GROUP)) {
+			return -EINVAL;
+		}
+	}
+
 	if (!(new = tcb_alloc_init()))
 		return -ENOMEM;
 
@@ -374,8 +369,7 @@ int thread_create(struct task_ids *ids, unsigned int flags)
 		goto out_err;
 
 	/* Obtain parent thread if there is one */
-	if (flags == THREAD_SAME_SPACE ||
-	    flags == THREAD_COPY_SPACE) {
+	if (flags & TC_SHARE_SPACE || flags & TC_COPY_SPACE) {
 		if (!(parent = tcb_find(ids->tid))) {
 			err = -EINVAL;
 			goto out_err;