diff --git a/packages/core/src/tools/modifiable-tool.test.ts b/packages/core/src/tools/modifiable-tool.test.ts
index 850da02b..d2672920 100644
--- a/packages/core/src/tools/modifiable-tool.test.ts
+++ b/packages/core/src/tools/modifiable-tool.test.ts
@@ -326,7 +326,7 @@ describe('modifyWithEditor', () => {
     consoleErrorSpy.mockRestore();
   });
 
-  it('should create temp files with correct naming', async () => {
+  it('should create temp files with correct naming with extension', async () => {
     const testFilePath = path.join(tempDir, 'subfolder', 'test-file.txt');
     mockModifyContext.getFilePath = vi.fn().mockReturnValue(testFilePath);
 
@@ -343,8 +343,31 @@ describe('modifyWithEditor', () => {
     const oldFilePath = writeFileCalls[0][0];
     const newFilePath = writeFileCalls[1][0];
 
-    expect(oldFilePath).toMatch(/gemini-cli-modify-test-file\.txt-old-\d+$/);
-    expect(newFilePath).toMatch(/gemini-cli-modify-test-file\.txt-new-\d+$/);
+    expect(oldFilePath).toMatch(/gemini-cli-modify-test-file-old-\d+\.txt$/);
+    expect(newFilePath).toMatch(/gemini-cli-modify-test-file-new-\d+\.txt$/);
+    expect(oldFilePath).toContain(`${tempDir}/gemini-cli-tool-modify-diffs/`);
+    expect(newFilePath).toContain(`${tempDir}/gemini-cli-tool-modify-diffs/`);
+  });
+
+  it('should create temp files with correct naming without extension', async () => {
+    const testFilePath = path.join(tempDir, 'subfolder', 'test-file');
+    mockModifyContext.getFilePath = vi.fn().mockReturnValue(testFilePath);
+
+    await modifyWithEditor(
+      mockParams,
+      mockModifyContext,
+      'vscode' as EditorType,
+      abortSignal,
+    );
+
+    const writeFileCalls = (fs.writeFileSync as Mock).mock.calls;
+    expect(writeFileCalls).toHaveLength(2);
+
+    const oldFilePath = writeFileCalls[0][0];
+    const newFilePath = writeFileCalls[1][0];
+
+    expect(oldFilePath).toMatch(/gemini-cli-modify-test-file-old-\d+$/);
+    expect(newFilePath).toMatch(/gemini-cli-modify-test-file-new-\d+$/);
     expect(oldFilePath).toContain(`${tempDir}/gemini-cli-tool-modify-diffs/`);
     expect(newFilePath).toContain(`${tempDir}/gemini-cli-tool-modify-diffs/`);
   });
diff --git a/packages/core/src/tools/modifiable-tool.ts b/packages/core/src/tools/modifiable-tool.ts
index e935a704..419aafeb 100644
--- a/packages/core/src/tools/modifiable-tool.ts
+++ b/packages/core/src/tools/modifiable-tool.ts
@@ -58,15 +58,16 @@ function createTempFilesForModify(
     fs.mkdirSync(diffDir, { recursive: true });
   }
 
-  const fileName = path.basename(file_path);
+  const ext = path.extname(file_path);
+  const fileName = path.basename(file_path, ext);
   const timestamp = Date.now();
   const tempOldPath = path.join(
     diffDir,
-    `gemini-cli-modify-${fileName}-old-${timestamp}`,
+    `gemini-cli-modify-${fileName}-old-${timestamp}${ext}`,
   );
   const tempNewPath = path.join(
     diffDir,
-    `gemini-cli-modify-${fileName}-new-${timestamp}`,
+    `gemini-cli-modify-${fileName}-new-${timestamp}${ext}`,
   );
 
   fs.writeFileSync(tempOldPath, currentContent, 'utf8');