diff --git a/src/backend/utils/mmgr/slab.c b/src/backend/utils/mmgr/slab.c
index ae1a735b8c..67fbede836 100644
--- a/src/backend/utils/mmgr/slab.c
+++ b/src/backend/utils/mmgr/slab.c
@@ -102,10 +102,10 @@ typedef struct SlabBlock
 #define SlabChunkGetPointer(chk)	\
 	((void *)(((char *)(chk)) + sizeof(MemoryChunk)))
 #define SlabBlockGetChunk(slab, block, idx) \
-	((MemoryChunk *) ((char *) (block) + sizeof(SlabBlock)	\
+	((MemoryChunk *) ((char *) (block) + MAXALIGN(sizeof(SlabBlock))	\
 					+ (idx * slab->fullChunkSize)))
 #define SlabBlockStart(block)	\
-	((char *) block + sizeof(SlabBlock))
+	((char *) block + MAXALIGN(sizeof(SlabBlock)))
 #define SlabChunkIndex(slab, block, chunk)	\
 	(((char *) chunk - SlabBlockStart(block)) / slab->fullChunkSize)
 
@@ -146,12 +146,12 @@ SlabContextCreate(MemoryContext parent,
 	fullChunkSize = Slab_CHUNKHDRSZ + MAXALIGN(chunkSize);
 
 	/* Make sure the block can store at least one chunk. */
-	if (blockSize < fullChunkSize + sizeof(SlabBlock))
+	if (blockSize < fullChunkSize + MAXALIGN(sizeof(SlabBlock)))
 		elog(ERROR, "block size %zu for slab is too small for %zu chunks",
 			 blockSize, chunkSize);
 
 	/* Compute maximum number of chunks per block */
-	chunksPerBlock = (blockSize - sizeof(SlabBlock)) / fullChunkSize;
+	chunksPerBlock = (blockSize - MAXALIGN(sizeof(SlabBlock))) / fullChunkSize;
 
 	/* The freelist starts with 0, ends with chunksPerBlock. */
 	freelistSize = sizeof(dlist_head) * (chunksPerBlock + 1);