diff --git a/src/backend/nodes/bitmapset.c b/src/backend/nodes/bitmapset.c
index 786f343b3c9..912a1ab696a 100644
--- a/src/backend/nodes/bitmapset.c
+++ b/src/backend/nodes/bitmapset.c
@@ -1289,6 +1289,7 @@ bms_join(Bitmapset *a, Bitmapset *b)
 int
 bms_next_member(const Bitmapset *a, int prevbit)
 {
+	int64		currbit;
 	int			nwords;
 	bitmapword	mask;
 
@@ -1297,13 +1298,13 @@ bms_next_member(const Bitmapset *a, int prevbit)
 	if (a == NULL)
 		return -2;
 	nwords = a->nwords;
-	prevbit++;
-	mask = (~(bitmapword) 0) << BITNUM(prevbit);
-	for (int wordnum = WORDNUM(prevbit); wordnum < nwords; wordnum++)
+	currbit = (int64) prevbit + 1;
+	mask = (~(bitmapword) 0) << BITNUM(currbit);
+	for (int wordnum = WORDNUM(currbit); wordnum < nwords; wordnum++)
 	{
 		bitmapword	w = a->words[wordnum];
 
-		/* ignore bits before prevbit */
+		/* ignore bits before currbit */
 		w &= mask;
 
 		if (w != 0)