diff --git a/CHANGELOG.md b/CHANGELOG.md
index cfdc166..094831b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,13 @@ All notable changes to `bgit` are documented in this file.
 
 This project follows semantic versioning.
 
+## 1.3.1
+
+Fixed
+
+- Guarded oversized local and web diff/index allocation paths to avoid integer
+  overflow in pathological repositories.
+
 ## 1.3.0
 
 Added
diff --git a/local_extra.go b/local_extra.go
index 54d7927..b0a77b1 100644
--- a/local_extra.go
+++ b/local_extra.go
@@ -1216,7 +1216,7 @@ func simpleLineDiff(left, right string) []string {
 	if left == right {
 		return nil
 	}
-	if len(a) != 0 && len(b) > 900000/len(a) {
+	if simpleLineDiffShouldFallback(len(a), len(b)) {
 		return simpleWholeFileDiff(a, b)
 	}
 	ops := simpleLineDiffOps(a, b)
@@ -1245,9 +1245,14 @@ type simpleDiffHunk struct {
 }
 
 func simpleLineDiffOps(a, b []string) []simpleDiffOp {
-	rows := make([][]int, len(a)+1)
+	if simpleLineDiffShouldFallback(len(a), len(b)) {
+		return simpleWholeFileDiffOps(a, b)
+	}
+	rowCount := len(a) + 1
+	colCount := len(b) + 1
+	rows := make([][]int, rowCount)
 	for i := range rows {
-		rows[i] = make([]int, len(b)+1)
+		rows[i] = make([]int, colCount)
 	}
 	for i := len(a) - 1; i >= 0; i-- {
 		for j := len(b) - 1; j >= 0; j-- {
@@ -1279,6 +1284,29 @@ func simpleLineDiffOps(a, b []string) []simpleDiffOp {
 	return ops
 }
 
+func simpleLineDiffShouldFallback(leftLines, rightLines int) bool {
+	const maxSimpleDiffCells = 900000
+	maxInt := int(^uint(0) >> 1)
+	if leftLines >= maxInt || rightLines >= maxInt {
+		return true
+	}
+	if leftLines != 0 && rightLines > maxSimpleDiffCells/leftLines {
+		return true
+	}
+	return false
+}
+
+func simpleWholeFileDiffOps(a, b []string) []simpleDiffOp {
+	var ops []simpleDiffOp
+	for i, line := range a {
+		ops = append(ops, simpleDiffOp{kind: '-', text: line, oldLine: i + 1})
+	}
+	for i, line := range b {
+		ops = append(ops, simpleDiffOp{kind: '+', text: line, newLine: i + 1})
+	}
+	return ops
+}
+
 func simpleLineDiffHunks(ops []simpleDiffOp, context int) []simpleDiffHunk {
 	var hunks []simpleDiffHunk
 	for i, op := range ops {
diff --git a/web.go b/web.go
index a917be7..17a1b6e 100644
--- a/web.go
+++ b/web.go
@@ -3875,7 +3875,8 @@ func (s *webServer) fileIndexHTML(ctx context.Context, treeHash, ref string) str
 	if len(paths) > maxInt-len(dirPaths) {
 		return ""
 	}
-	index := make([]webFileIndexEntry, 0, len(paths)+len(dirPaths))
+	indexLen := len(paths) + len(dirPaths)
+	index := make([]webFileIndexEntry, 0, indexLen)
 	for _, dir := range dirPaths {
 		index = append(index, webFileIndexEntry{Path: dir, URL: webURL("tree", dir, ref), Kind: "dir"})
 	}