diff --git a/src/memheap.c b/src/memheap.c
index 68a15d1a8e4..e96b402bcf6 100644
--- a/src/memheap.c
+++ b/src/memheap.c
@@ -832,13 +832,16 @@ static struct rt_memheap _heap;
  */
 void rt_system_heap_init(void *begin_addr, void *end_addr)
 {
-    RT_ASSERT((rt_uint32_t)end_addr > (rt_uint32_t)begin_addr);
+    RT_ASSERT((rt_size_t)end_addr > (rt_size_t)begin_addr);
+
+    rt_size_t begin_align = RT_ALIGN((rt_size_t)begin_addr, RT_ALIGN_SIZE);
+    rt_size_t end_align   = RT_ALIGN_DOWN((rt_size_t)end_addr, RT_ALIGN_SIZE);
 
     /* initialize a default heap in the system */
     rt_memheap_init(&_heap,
                     "heap",
-                    begin_addr,
-                    (rt_uint32_t)end_addr - (rt_uint32_t)begin_addr);
+                    (void *)begin_align,
+                    end_align - begin_align);
 }
 
 /**
@@ -850,6 +853,10 @@ void *rt_malloc(rt_size_t size)
 {
     void *ptr;
 
+    /* zero size, return RT_NULL */
+    if (size == 0)
+        return RT_NULL;
+
     /* try to allocate in system heap */
     ptr = rt_memheap_alloc(&_heap, size);
 #ifdef RT_USING_MEMHEAP_AUTO_BINDING