diff --git a/lib/slicesutil/slicesutil.go b/lib/slicesutil/slicesutil.go
new file mode 100644
index 000000000..4ce954224
--- /dev/null
+++ b/lib/slicesutil/slicesutil.go
@@ -0,0 +1,10 @@
+package slicesutil
+
+// ExtendCapacity returns a with the capacity extended to len(a)+n if needed.
+func ExtendCapacity[T any](a []T, n int) []T {
+	aLen := len(a)
+	if n := aLen + n - cap(a); n > 0 {
+		a = append(a[:cap(a)], make([]T, n)...)
+	}
+	return a[:aLen]
+}