Index: kernel/generic/src/cap/cap.c
===================================================================
--- kernel/generic/src/cap/cap.c	(revision c1f68b0b464a5358c1ef12ca16a6a4fb18b3ad5a)
+++ kernel/generic/src/cap/cap.c	(revision 98cb5e0d438f111dd28c92d57d12c9aa74bd2f98)
@@ -73,4 +73,5 @@
 
 #include <cap/cap.h>
+#include <abi/cap.h>
 #include <proc/task.h>
 #include <synch/mutex.h>
@@ -81,5 +82,7 @@
 #include <stdint.h>
 
-#define MAX_CAPS	INT_MAX
+#define CAPS_START	(CAP_NIL + 1)
+#define CAPS_SIZE	(INT_MAX - CAPS_START)
+#define CAPS_LAST	(CAPS_SIZE - 1)
 
 static slab_cache_t *cap_slab;
@@ -129,5 +132,5 @@
 	if (!task->cap_info->handles)
 		goto error_handles;
-	if (!ra_span_add(task->cap_info->handles, 0, MAX_CAPS))
+	if (!ra_span_add(task->cap_info->handles, CAPS_START, CAPS_SIZE))
 		goto error_span;
 	if (!hash_table_create(&task->cap_info->caps, 0, 0, &caps_ops))
@@ -220,5 +223,5 @@
 	assert(mutex_locked(&task->cap_info->lock));
 
-	if ((handle < 0) || (handle >= MAX_CAPS))
+	if ((handle < CAPS_START) || (handle > CAPS_LAST))
 		return NULL;
 	ht_link_t *link = hash_table_find(&task->cap_info->caps, &handle);
@@ -357,6 +360,6 @@
 void cap_free(task_t *task, cap_handle_t handle)
 {
-	assert(handle >= 0);
-	assert(handle < MAX_CAPS);
+	assert(handle >= CAPS_START);
+	assert(handle <= CAPS_LAST);
 
 	mutex_lock(&task->cap_info->lock);