diff --git a/src/core/mem.c b/src/core/mem.c
index 1e376b49..2ee5cfc7 100644
--- a/src/core/mem.c
+++ b/src/core/mem.c
@@ -586,7 +586,7 @@ mem_malloc(mem_size_t size)
         LWIP_ASSERT("mem_malloc: allocated memory not above ram_end.",
          (mem_ptr_t)mem + SIZEOF_STRUCT_MEM + size <= (mem_ptr_t)ram_end);
         LWIP_ASSERT("mem_malloc: allocated memory properly aligned.",
-         (unsigned long)((u8_t *)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);
+         ((mem_ptr_t)mem + SIZEOF_STRUCT_MEM) % MEM_ALIGNMENT == 0);
         LWIP_ASSERT("mem_malloc: sanity check alignment",
           (((mem_ptr_t)mem) & (MEM_ALIGNMENT-1)) == 0);