diff --git a/fs/btrfs/extent_map.c b/fs/btrfs/extent_map.c
index a042a193c120..928f729c55ba 100644
--- a/fs/btrfs/extent_map.c
+++ b/fs/btrfs/extent_map.c
@@ -210,6 +210,9 @@ static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 	if (!list_empty(&prev->list) || !list_empty(&next->list))
 		return 0;
 
+	ASSERT(next->block_start != EXTENT_MAP_DELALLOC &&
+	       prev->block_start != EXTENT_MAP_DELALLOC);
+
 	if (extent_map_end(prev) == next->start &&
 	    prev->flags == next->flags &&
 	    prev->bdev == next->bdev &&
@@ -217,8 +220,6 @@ static int mergable_maps(struct extent_map *prev, struct extent_map *next)
 	      prev->block_start == EXTENT_MAP_HOLE) ||
 	     (next->block_start == EXTENT_MAP_INLINE &&
 	      prev->block_start == EXTENT_MAP_INLINE) ||
-	     (next->block_start == EXTENT_MAP_DELALLOC &&
-	      prev->block_start == EXTENT_MAP_DELALLOC) ||
 	     (next->block_start < EXTENT_MAP_LAST_BYTE - 1 &&
 	      next->block_start == extent_map_block_end(prev)))) {
 		return 1;
diff --git a/fs/btrfs/extent_map.h b/fs/btrfs/extent_map.h
index ef05a0121652..473f039fcd7c 100644
--- a/fs/btrfs/extent_map.h
+++ b/fs/btrfs/extent_map.h
@@ -9,6 +9,7 @@
 #define EXTENT_MAP_LAST_BYTE ((u64)-4)
 #define EXTENT_MAP_HOLE ((u64)-3)
 #define EXTENT_MAP_INLINE ((u64)-2)
+/* used only during fiemap calls */
 #define EXTENT_MAP_DELALLOC ((u64)-1)
 
 /* bits for the extent_map::flags field */