From 2e734707edfbf183f818fde2d5514845177d2774 Mon Sep 17 00:00:00 2001
From: Petyo Ivanov <underlog@gmail.com>
Date: Wed, 26 Apr 2023 14:46:46 +0300
Subject: [PATCH] fix: edge case with a single group

Fixes #886
---
 src/sizeSystem.ts            | 3 ++-
 src/upwardScrollFixSystem.ts | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/sizeSystem.ts b/src/sizeSystem.ts
index 9bc4a4c6d..b9fd772ed 100644
--- a/src/sizeSystem.ts
+++ b/src/sizeSystem.ts
@@ -459,7 +459,8 @@ export const sizeSystem = u.system(
 
             while (prependedGroupItemsCount < unshiftWith) {
               const theGroupIndex = sizes.groupIndices[groupIndex]
-              const groupItemCount = sizes.groupIndices[groupIndex + 1] - theGroupIndex - 1
+              const groupItemCount =
+                sizes.groupIndices.length === groupIndex + 1 ? Infinity : sizes.groupIndices[groupIndex + 1] - theGroupIndex - 1
 
               initialRanges.push({
                 startIndex: theGroupIndex,
diff --git a/src/upwardScrollFixSystem.ts b/src/upwardScrollFixSystem.ts
index 46861d398..54110b430 100644
--- a/src/upwardScrollFixSystem.ts
+++ b/src/upwardScrollFixSystem.ts
@@ -124,7 +124,8 @@ export const upwardScrollFixSystem = u.system(
               recognizedOffsetItems++
               amount += defaultGroupSize
 
-              let groupItemCount = groupIndices[groupIndex + 1] - groupIndices[groupIndex] - 1
+              let groupItemCount =
+                groupIndices.length === groupIndex + 1 ? Infinity : groupIndices[groupIndex + 1] - groupIndices[groupIndex] - 1
 
               // if the group is larger than the offset, we have an expanded group. remove the group size, and replace with 1 item.
               if (recognizedOffsetItems + groupItemCount > offset) {