diff --git a/src/backend/access/nbtree/nbtutils.c b/src/backend/access/nbtree/nbtutils.c
index 8381027f4e..05f0d23dc0 100644
--- a/src/backend/access/nbtree/nbtutils.c
+++ b/src/backend/access/nbtree/nbtutils.c
@@ -2572,19 +2572,16 @@ _bt_preprocess_keys(IndexScanDesc scan)
 	int		   *keyDataMap = NULL;
 	int			arrayidx = 0;
 
-	/*
-	 * We're called at the start of each primitive index scan during scans
-	 * that use equality array keys.  We can just reuse the scan keys that
-	 * were output at the start of the scan's first primitive index scan.
-	 */
 	if (so->numberOfKeys > 0)
 	{
 		/*
-		 * An earlier call to _bt_advance_array_keys already set everything up
-		 * already.  Just assert that the scan's existing output scan keys are
-		 * consistent with its current array elements.
+		 * Only need to do preprocessing once per btrescan, at most.  All
+		 * calls after the first are handled as no-ops.
+		 *
+		 * If there are array scan keys in so->keyData[], then the now-current
+		 * array elements must already be present in each array's scan key.
+		 * Verify that that happened using an assertion.
 		 */
-		Assert(so->numArrayKeys);
 		Assert(_bt_verify_keys_with_arraykeys(scan));
 		return;
 	}