diff --git a/conts/libl4/include/l4lib/arch-arm/syscalls.h b/conts/libl4/include/l4lib/arch-arm/syscalls.h
index 09b1c62..584da7a 100644
--- a/conts/libl4/include/l4lib/arch-arm/syscalls.h
+++ b/conts/libl4/include/l4lib/arch-arm/syscalls.h
@@ -16,9 +16,10 @@
 #include <l4/api/thread.h>
 
 struct task_ids {
-	int tid;
-	int spid;
-	int tgid;
+	l4id_t tid;
+	l4id_t spid;
+	l4id_t tgid;
+	l4id_t cid;
 };
 
 static inline void *
diff --git a/conts/libl4/include/l4lib/arch-arm/types.h b/conts/libl4/include/l4lib/arch-arm/types.h
index f01616b..76dc5ba 100644
--- a/conts/libl4/include/l4lib/arch-arm/types.h
+++ b/conts/libl4/include/l4lib/arch-arm/types.h
@@ -1,7 +1,7 @@
 #ifndef __L4LIB_ARM_TYPES_H___
 #define __L4LIB_ARM_TYPES_H__
 
-#define TASK_ID_INVALID			-1
+#define TASK_ID_INVALID			0xFFFFFFFF
 
 #include <l4/arch/arm/types.h>
 
diff --git a/conts/posix/mm0/mm/init.c b/conts/posix/mm0/mm/init.c
index aa1eda8..51e65a6 100644
--- a/conts/posix/mm0/mm/init.c
+++ b/conts/posix/mm0/mm/init.c
@@ -226,13 +226,11 @@ int read_pager_capabilities()
 	/* Set up pointers to important capabilities */
 	list_foreach_struct(cap, &capability_list.caps, list) {
 		/* Physical memory bank */
-		if ((cap->type & CAP_RTYPE_MASK)
-		    == CAP_RTYPE_PHYSMEM)
+		if (cap_type(cap) == CAP_TYPE_MAP_PHYSMEM)
 			cont_mem_regions.physmem = cap;
 
 		/* Virtual regions */
-		if ((cap->type & CAP_RTYPE_MASK)
-		    == CAP_RTYPE_VIRTMEM) {
+		if (cap_type(cap) == CAP_TYPE_MAP_VIRTMEM) {
 
 			/* Pager address region (get from linker-defined) */
 			if (__pfn_to_addr(cap->start)
diff --git a/conts/posix/test0/main.c b/conts/posix/test0/main.c
index eeba774..fdd97b9 100644
--- a/conts/posix/test0/main.c
+++ b/conts/posix/test0/main.c
@@ -26,7 +26,7 @@ void wait_pager(l4id_t partner)
 }
 
 pid_t parent_of_all;
-pid_t pagerid;
+l4id_t pagerid;
 
 int main(int argc, char *argv[])
 {
diff --git a/conts/posix/test0/src/test_exec/test_exec.c b/conts/posix/test0/src/test_exec/test_exec.c
index 3eb42b2..41695a1 100644
--- a/conts/posix/test0/src/test_exec/test_exec.c
+++ b/conts/posix/test0/src/test_exec/test_exec.c
@@ -24,7 +24,7 @@ void wait_pager(l4id_t partner)
 	// printf("Pager synced with us.\n");
 }
 
-pid_t pagerid;
+l4id_t pagerid;
 
 int main(int argc, char *argv[])
 {
diff --git a/conts/test/main.c b/conts/test/main.c
index 12ea2b7..aaa03ed 100644
--- a/conts/test/main.c
+++ b/conts/test/main.c
@@ -66,12 +66,12 @@ int main(void)
 	printf("%s: Container %s started\n",
 	       __CONTAINER__, __CONTAINER_NAME__);
 
-	//capability_test();
+	capability_test();
 
-	exit_test();
+	//exit_test();
 
 	/* Now quit to demo self-paging quit */
-	l4_exit(0);
+	//l4_exit(0);
 
 	/* Now quit by null pointer */
 	//	*((int *)0) = 5;
diff --git a/include/l4/api/ipc.h b/include/l4/api/ipc.h
index 22be162..08ffedf 100644
--- a/include/l4/api/ipc.h
+++ b/include/l4/api/ipc.h
@@ -2,8 +2,8 @@
 #define __IPC_H__
 
 
-#define L4_NILTHREAD		-1
-#define L4_ANYTHREAD		-2
+#define L4_NILTHREAD		0xFFFFFFFF
+#define L4_ANYTHREAD		0xFFFFFFFE
 
 #define L4_IPC_TAG_MR_OFFSET		0
 
diff --git a/include/l4/arch/arm/types.h b/include/l4/arch/arm/types.h
index 4c5df35..3106d6c 100644
--- a/include/l4/arch/arm/types.h
+++ b/include/l4/arch/arm/types.h
@@ -12,7 +12,7 @@ typedef signed short s16;
 typedef signed char s8;
 
 /* Thread/Space id type */
-typedef int l4id_t;
+typedef unsigned int l4id_t;
 
 #endif /* !__ASSEMBLY__ */
 #endif /* !__ARCH_TYPES_H__ */
diff --git a/include/l4/generic/tcb.h b/include/l4/generic/tcb.h
index 4dceb95..ab707d0 100644
--- a/include/l4/generic/tcb.h
+++ b/include/l4/generic/tcb.h
@@ -39,11 +39,21 @@ enum task_state {
 	TASK_DEAD	= 3,
 };
 
-#define TASK_ID_INVALID			-1
+#define TASK_CID_MASK			0xFF000000
+#define TASK_ID_MASK			0x00FFFFFF
+
+static inline int task_id_special(l4id_t id)
+{
+	/* Special ids have top 2 nibbles all set */
+	return (id & TASK_CID_MASK) == TASK_CID_MASK;
+}
+
+#define TASK_ID_INVALID			0xFFFFFFFF
 struct task_ids {
 	l4id_t tid;
 	l4id_t spid;
 	l4id_t tgid;
+	l4id_t cid;
 };
 
 struct container;
diff --git a/src/api/ipc.c b/src/api/ipc.c
index 0b99f19..020ee14 100644
--- a/src/api/ipc.c
+++ b/src/api/ipc.c
@@ -539,11 +539,14 @@ int sys_ipc(l4id_t to, l4id_t from, unsigned int flags)
 	int ret = 0;
 
 	/* Check arguments */
-	if (from < L4_ANYTHREAD) {
+	if (task_id_special(from) &&
+	    from != L4_ANYTHREAD && from != L4_NILTHREAD) {
 		ret = -EINVAL;
 		goto error;
 	}
-	if (to < L4_ANYTHREAD) {
+
+	if (task_id_special(to) &&
+	    to != L4_ANYTHREAD && to != L4_NILTHREAD) {
 		ret = -EINVAL;
 		goto error;
 	}
diff --git a/src/api/syscall.c b/src/api/syscall.c
index 1ff2769..94fea02 100644
--- a/src/api/syscall.c
+++ b/src/api/syscall.c
@@ -48,6 +48,7 @@ int sys_getid(struct task_ids *ids)
 	ids->tid = this->tid;
 	ids->spid = this->space->spid;
 	ids->tgid = this->tgid;
+	ids->cid = this->container->cid;
 
 	return 0;
 }