diff --git a/open-sse/translator/response/openai-responses.ts b/open-sse/translator/response/openai-responses.ts
index 40b3b67076..ebd417d007 100644
--- a/open-sse/translator/response/openai-responses.ts
+++ b/open-sse/translator/response/openai-responses.ts
@@ -16,7 +16,7 @@ function stripEmptyOptionalToolArgs(value) {
     try {
       const parsed = JSON.parse(value);
       const cleaned = stripEmptyOptionalToolArgs(parsed);
-      return JSON.stringify(cleaned || {});
+      return JSON.stringify(cleaned ?? {});
     } catch {
       return value;
     }
diff --git a/tests/unit/translator-resp-openai-responses.test.ts b/tests/unit/translator-resp-openai-responses.test.ts
index 2d6706b316..569cfa5f0d 100644
--- a/tests/unit/translator-resp-openai-responses.test.ts
+++ b/tests/unit/translator-resp-openai-responses.test.ts
@@ -242,6 +242,26 @@ test("Responses -> OpenAI: empty-name tool call is deferred until output_item.do
   );
 });
 
+test("Responses -> OpenAI: preserves falsy JSON-string tool arguments while cleaning", () => {
+  const state = {};
+  openaiResponsesToOpenAIResponse(
+    {
+      type: "response.output_item.added",
+      item: { type: "function_call", call_id: "call_flag", name: "set_flag" },
+    },
+    state
+  );
+  const done = openaiResponsesToOpenAIResponse(
+    {
+      type: "response.output_item.done",
+      item: { type: "function_call", call_id: "call_flag", name: "set_flag", arguments: "false" },
+    },
+    state
+  );
+
+  assert.equal(done.choices[0].delta.tool_calls[0].function.arguments, "false");
+});
+
 test("Responses -> OpenAI: strips empty optional args from JSON-string output_item.done arguments", () => {
   const state = {};
   openaiResponsesToOpenAIResponse(