diff --git a/src/backend/utils/mmgr/aset.c b/src/backend/utils/mmgr/aset.c
index 3c5d651..ae733d8 100644
--- a/src/backend/utils/mmgr/aset.c
+++ b/src/backend/utils/mmgr/aset.c
@@ -860,17 +860,16 @@ AllocSetAlloc(MemoryContext context, Size size)
 		 * We could be asking for pretty big blocks here, so cope if malloc
 		 * fails.  But give up if there's less than a meg or so available...
 		 */
-		while (block == NULL && blksize > 1024 * 1024)
+		while (block == NULL)
 		{
 			blksize >>= 1;
-			if (blksize < required_size)
-				break;
+
+			/* has the block size gotten too small? */
+			if (blksize < required_size || blksize <= 1024 * 1024)
+				return NULL;
 			block = (AllocBlock) malloc(blksize);
 		}
 
-		if (block == NULL)
-			return NULL;
-
 		context->mem_allocated += blksize;
 
 		block->aset = set;