diff --git a/kernel/mem_slab.c b/kernel/mem_slab.c
index 8efcd156420..7e3765dd372 100644
--- a/kernel/mem_slab.c
+++ b/kernel/mem_slab.c
@@ -33,6 +33,11 @@ static void create_free_list(struct k_mem_slab *slab)
 	u32_t j;
 	char *p;
 
+	/* blocks must be word aligned */
+	__ASSERT(((slab->block_size | (uintptr_t)slab->buffer)
+					& (sizeof(void *) - 1)) == 0,
+		 "slab at %p not word aligned", slab);
+
 	slab->free_list = NULL;
 	p = slab->buffer;
 
@@ -68,10 +73,6 @@ SYS_INIT(init_mem_slab_module, PRE_KERNEL_1,
 void k_mem_slab_init(struct k_mem_slab *slab, void *buffer,
 		    size_t block_size, u32_t num_blocks)
 {
-	/* block size must be word aligned */
-	__ASSERT((slab->block_size & (sizeof(void *) - 1)) == 0,
-		 "block size not word aligned");
-
 	slab->num_blocks = num_blocks;
 	slab->block_size = block_size;
 	slab->buffer = buffer;
@@ -88,10 +89,6 @@ int k_mem_slab_alloc(struct k_mem_slab *slab, void **mem, s32_t timeout)
 	k_spinlock_key_t key = k_spin_lock(&lock);
 	int result;
 
-	/* block size must be word aligned */
-	__ASSERT((slab->block_size & (sizeof(void *) - 1)) == 0,
-		 "block size not word aligned");
-
 	if (slab->free_list != NULL) {
 		/* take a free block */
 		*mem = slab->free_list;