diff --git a/src/mem.c b/src/mem.c
index ac0d27f2c35d4dd8e830b48ad07f2f108a07e69a..2b4d3a03bed88ae42049aed3bc081c65a345f154 100644
--- a/src/mem.c
+++ b/src/mem.c
@@ -250,7 +250,7 @@ void rt_system_heap_init(void *begin_addr, void *end_addr)
     rt_mem_setname(heap_end, "INIT");
 #endif
 
-    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_FIFO);
+    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_PRIO);
 
     /* initialize the lowest-free pointer to the start of the heap */
     lfree = (struct heap_mem *)heap_ptr;
diff --git a/src/memheap.c b/src/memheap.c
index 35a04c14b16e17f8a304730dc39be6a179d086a2..d3ad6d2c362c34acc7c927ab8548d818a3984cba 100644
--- a/src/memheap.c
+++ b/src/memheap.c
@@ -155,7 +155,7 @@ rt_err_t rt_memheap_init(struct rt_memheap *memheap,
     item->next_free = item->prev_free = RT_NULL;
 
     /* initialize semaphore lock */
-    rt_sem_init(&(memheap->lock), name, 1, RT_IPC_FLAG_FIFO);
+    rt_sem_init(&(memheap->lock), name, 1, RT_IPC_FLAG_PRIO);
 
     RT_DEBUG_LOG(RT_DEBUG_MEMHEAP,
                  ("memory heap: start addr 0x%08x, size %d, free list header 0x%08x\n",
diff --git a/src/slab.c b/src/slab.c
index 114259002f848ef6093a88d936311ff5bd95fb34..2769892b68b54ea4b88e6c6d1d9fa32544608027 100644
--- a/src/slab.c
+++ b/src/slab.c
@@ -363,7 +363,7 @@ void rt_system_heap_init(void *begin_addr, void *end_addr)
     npages  = limsize / RT_MM_PAGE_SIZE;
 
     /* initialize heap semaphore */
-    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_FIFO);
+    rt_sem_init(&heap_sem, "heap", 1, RT_IPC_FLAG_PRIO);
 
     RT_DEBUG_LOG(RT_DEBUG_SLAB, ("heap[0x%x - 0x%x], size 0x%x, 0x%x pages\n",
                                  heap_start, heap_end, limsize, npages));