diff --git a/action/index.cjs b/action/index.cjs
index f199b2b..bbcf676 100644
--- a/action/index.cjs
+++ b/action/index.cjs
@@ -147441,6 +147441,7 @@ class Chat {
         console.time('code-review cost');
         const prompt = this.generatePrompt(patch);
         const isReasoning = this.isReasoningModel;
+        const temperature = Number(process.env.temperature || 1);
         const res = await this.openai.chat.completions.create({
             messages: [
                 {
@@ -147450,7 +147451,7 @@ class Chat {
             ],
             model: this.model,
             ...(isReasoning ? {} : {
-                temperature: +(process.env.temperature || 0) || 1,
+                temperature: Number.isFinite(temperature) ? temperature : 1,
                 top_p: +(process.env.top_p || 0) || 1,
             }),
             max_tokens: process.env.max_tokens ? +process.env.max_tokens : undefined,
diff --git a/src/chat.ts b/src/chat.ts
index 408cb1c..f506e9f 100644
--- a/src/chat.ts
+++ b/src/chat.ts
@@ -99,6 +99,7 @@ export class Chat {
     const prompt = this.generatePrompt(patch);
 
     const isReasoning = this.isReasoningModel;
+    const temperature = Number(process.env.temperature || 1);
 
     const res = await this.openai.chat.completions.create({
       messages: [
@@ -109,7 +110,7 @@ export class Chat {
       ],
       model: this.model,
       ...(isReasoning ? {} : {
-        temperature: +(process.env.temperature || 0) || 1,
+        temperature: Number.isFinite(temperature) ? temperature : 1,
         top_p: +(process.env.top_p || 0) || 1,
       }),
       max_tokens: process.env.max_tokens ? +process.env.max_tokens : undefined,
diff --git a/test/chat.test.ts b/test/chat.test.ts
index 527534c..4df5697 100644
--- a/test/chat.test.ts
+++ b/test/chat.test.ts
@@ -218,6 +218,23 @@ describe("Chat", () => {
     expect(callArgs.response_format).toEqual({ type: "json_object" });
   });
 
+  test.each(["0", "0.0"])("preserves zero temperature %s", async (temperature) => {
+    process.env.MODEL = "gpt-4o";
+    process.env.temperature = temperature;
+    const chat = new Chat("test-key");
+    await chat.codeReview("@@ -1 +1 @@\n-old\n+new");
+    expect(mockCreate.mock.calls[0][0].temperature).toBe(0);
+  });
+
+  test.each([undefined, "", "invalid"])("defaults temperature %s to one", async (temperature) => {
+    process.env.MODEL = "gpt-4o";
+    if (temperature === undefined) delete process.env.temperature;
+    else process.env.temperature = temperature;
+    const chat = new Chat("test-key");
+    await chat.codeReview("@@ -1 +1 @@\n-old\n+new");
+    expect(mockCreate.mock.calls[0][0].temperature).toBe(1);
+  });
+
   test("returns empty review for empty patch", async () => {
     const chat = new Chat("test-key");
     const result = await chat.codeReview("");