diff --git a/src/include/access/gist_private.h b/src/include/access/gist_private.h
index 1a0e1ea72ed..058435cfe56 100644
--- a/src/include/access/gist_private.h
+++ b/src/include/access/gist_private.h
@@ -118,7 +118,7 @@ typedef struct GISTScanOpaqueData
 
 	/* pre-allocated workspace arrays */
 	GISTSearchTreeItem *tmpTreeItem;	/* workspace to pass to rb_insert */
-	double	   *distances;		/* workspace for computeKeyTupleDistance */
+	double	   *distances;		/* output area for gistindex_keytest */
 
 	/* In a non-ordered search, returnable heap items are stored here: */
 	GISTSearchHeapItem pageData[BLCKSZ / sizeof(IndexTupleData)];