diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c
index 7eeaafe2cb3..9ce628e62a5 100644
--- a/src/backend/access/transam/slru.c
+++ b/src/backend/access/transam/slru.c
@@ -343,7 +343,7 @@ SimpleLruInit(SlruCtl ctl, const char *name, int nslots, int nlsns,
 	ctl->shared = shared;
 	ctl->sync_handler = sync_handler;
 	ctl->long_segment_names = long_segment_names;
-	ctl->bank_mask = (nslots / SLRU_BANK_SIZE) - 1;
+	ctl->nbanks = nbanks;
 	strlcpy(ctl->Dir, subdir, sizeof(ctl->Dir));
 }
 
@@ -606,7 +606,7 @@ SimpleLruReadPage_ReadOnly(SlruCtl ctl, int64 pageno, TransactionId xid)
 {
 	SlruShared	shared = ctl->shared;
 	LWLock	   *banklock = SimpleLruGetBankLock(ctl, pageno);
-	int			bankno = pageno & ctl->bank_mask;
+	int			bankno = pageno % ctl->nbanks;
 	int			bankstart = bankno * SLRU_BANK_SIZE;
 	int			bankend = bankstart + SLRU_BANK_SIZE;
 
@@ -1180,7 +1180,7 @@ SlruSelectLRUPage(SlruCtl ctl, int64 pageno)
 		int			bestinvalidslot = 0;	/* keep compiler quiet */
 		int			best_invalid_delta = -1;
 		int64		best_invalid_page_number = 0;	/* keep compiler quiet */
-		int			bankno = pageno & ctl->bank_mask;
+		int			bankno = pageno % ctl->nbanks;
 		int			bankstart = bankno * SLRU_BANK_SIZE;
 		int			bankend = bankstart + SLRU_BANK_SIZE;
 
diff --git a/src/include/access/slru.h b/src/include/access/slru.h
index ae871b640f8..e142800aab2 100644
--- a/src/include/access/slru.h
+++ b/src/include/access/slru.h
@@ -128,10 +128,8 @@ typedef struct SlruCtlData
 {
 	SlruShared	shared;
 
-	/*
-	 * Bitmask to determine bank number from page number.
-	 */
-	bits16		bank_mask;
+	/* Number of banks in this SLRU. */
+	uint16		nbanks;
 
 	/*
 	 * If true, use long segment file names.  Otherwise, use short file names.
@@ -163,7 +161,6 @@ typedef struct SlruCtlData
 	 * it's always the same, it doesn't need to be in shared memory.
 	 */
 	char		Dir[64];
-
 } SlruCtlData;
 
 typedef SlruCtlData *SlruCtl;
@@ -179,7 +176,7 @@ SimpleLruGetBankLock(SlruCtl ctl, int64 pageno)
 {
 	int			bankno;
 
-	bankno = pageno & ctl->bank_mask;
+	bankno = pageno % ctl->nbanks;
 	return &(ctl->shared->bank_locks[bankno].lock);
 }