diff --git a/docs/en/releases/unreleased.ipynb b/docs/en/releases/unreleased.ipynb
index 2fb158d..a33d283 100644
--- a/docs/en/releases/unreleased.ipynb
+++ b/docs/en/releases/unreleased.ipynb
@@ -774,6 +774,10 @@
    "id": "dd292ce1",
    "metadata": {},
    "source": [
+    "### Fixed a bug where the sum of binary `{0, 1}` expressions had type Binary instead of Natural\n",
+    "\n",
+    "We fixed a bug where an expression that `sum`s another expression of binary type (`{0, 1}`) was typed as `Binary` instead of `Natural`. For example, the sum $\\sum_i x_i$ of binary variables $x_0, x_1, \\ldots$ can take values of $2$ or more, so the result type had to be `Natural` instead of `Binary`.\n",
+    "\n",
     "## Other Changes\n",
     "\n",
     "- Relaxed version bounds to allow installation on any Python 3 version from Python 3.11 onwards.\n",
diff --git a/docs/ja/releases/unreleased.ipynb b/docs/ja/releases/unreleased.ipynb
index 259a371..71adfc8 100644
--- a/docs/ja/releases/unreleased.ipynb
+++ b/docs/ja/releases/unreleased.ipynb
@@ -753,6 +753,10 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
+    "### バイナリ`{0, 1}`型の式の総和が自然数型ではなくバイナリ型になっていた問題を修正\n",
+    "\n",
+    "バイナリ型（`{0, 1}`）の式を `sum` で総和した式の型が `Natural` ではなく `Binary` になってしまっていた問題を修正しました。たとえば、バイナリ変数 $x_0, x_1, \\ldots$ の総和 $\\sum_i x_i$ は $0$ や $1$ だけでなく $2$ 以上の値も取りうるため、結果の型は `Binary` ではなく `Natural` であるべきです。\n",
+    "\n",
     "## その他の変更\n",
     "\n",
     "- バージョン条件を緩和し、Python 3.11 以降の任意の Python 3 でのインストールを許容しました。\n",
diff --git a/markdowns/en/releases/unreleased.md b/markdowns/en/releases/unreleased.md
index e0a6fd5..a33fe58 100644
--- a/markdowns/en/releases/unreleased.md
+++ b/markdowns/en/releases/unreleased.md
@@ -267,6 +267,10 @@ compiler = jm.Compiler.from_problem(problem, instance_data)
 instance = compiler.eval_problem(problem, constraint_detection=True)
 ```
 
+### Fixed a bug where the sum of binary `{0, 1}` expressions had type Binary instead of Natural
+
+We fixed a bug where an expression that `sum`s another expression of binary type (`{0, 1}`) was typed as `Binary` instead of `Natural`. For example, the sum $\sum_i x_i$ of binary variables $x_0, x_1, \ldots$ can take values of $2$ or more, so the result type had to be `Natural` instead of `Binary`.
+
 ## Other Changes
 
 - Relaxed version bounds to allow installation on any Python 3 version from Python 3.11 onwards.
diff --git a/markdowns/ja/releases/unreleased.md b/markdowns/ja/releases/unreleased.md
index 9e9a0a3..ea66c62 100644
--- a/markdowns/ja/releases/unreleased.md
+++ b/markdowns/ja/releases/unreleased.md
@@ -260,6 +260,10 @@ compiler = jm.Compiler.from_problem(problem, instance_data)
 instance = compiler.eval_problem(problem, constraint_detection=True)
 ```
 
+### バイナリ`{0, 1}`型の式の総和が自然数型ではなくバイナリ型になっていた問題を修正
+
+バイナリ型（`{0, 1}`）の式を `sum` で総和した式の型が `Natural` ではなく `Binary` になってしまっていた問題を修正しました。たとえば、バイナリ変数 $x_0, x_1, \ldots$ の総和 $\sum_i x_i$ は $0$ や $1$ だけでなく $2$ 以上の値も取りうるため、結果の型は `Binary` ではなく `Natural` であるべきです。
+
 ## その他の変更
 
 - バージョン条件を緩和し、Python 3.11 以降の任意の Python 3 でのインストールを許容しました。