diff --git a/parasite-syscall.c b/parasite-syscall.c
index e77579265..e92f1768d 100644
--- a/parasite-syscall.c
+++ b/parasite-syscall.c
@@ -239,7 +239,7 @@ static void *mmap_seized(struct parasite_ctl *ctl,
 
 	err = syscall_seized(ctl, __NR_mmap, &map,
 			(unsigned long)addr, length, prot, flags, fd, offset);
-	if (err < 0 || (long)map < 0)
+	if (err < 0 || map > TASK_SIZE)
 		map = 0;
 
 	return (void *)map;
diff --git a/pie/parasite.c b/pie/parasite.c
index fec12b044..1cd8c8127 100644
--- a/pie/parasite.c
+++ b/pie/parasite.c
@@ -45,7 +45,7 @@ static int brk_init(void)
 	ret = sys_mmap(NULL, MAX_HEAP_SIZE,
 			    PROT_READ | PROT_WRITE,
 			    MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
-	if (ret < 0)
+	if (ret > TASK_SIZE)
 		return -ENOMEM;
 
 	brk_start = brk_tail = (void *)ret;
@@ -427,7 +427,7 @@ static int init(struct parasite_init_args *args)
 				     PROT_READ | PROT_WRITE,
 				     MAP_PRIVATE | MAP_ANONYMOUS,
 				     -1, 0);
-	if ((long)tid_state < 0)
+	if ((unsigned long)tid_state > TASK_SIZE)
 		return -ENOMEM;
 
 	nr_tid_state = args->nr_threads;