diff --git a/packages/core/src/tools/grep.test.ts b/packages/core/src/tools/grep.test.ts
index 4af684b1cd..860169c02d 100644
--- a/packages/core/src/tools/grep.test.ts
+++ b/packages/core/src/tools/grep.test.ts
@@ -314,6 +314,34 @@ describe('GrepTool', () => {
       );
     }, 30000);
 
+    it('should pass -i flag to system grep for case-insensitivity', async () => {
+      vi.mocked(execStreaming).mockImplementationOnce(() =>
+        createLineGenerator(['fileA.txt:1:hello world']),
+      );
+
+      const params: GrepToolParams = { pattern: 'HELLO' };
+      const invocation = grepTool.build(params) as unknown as {
+        isCommandAvailable: (command: string) => Promise<boolean>;
+        execute: (options: ExecuteOptions) => Promise<ToolResult>;
+      };
+      // Force system grep strategy by mocking isCommandAvailable and ensuring git grep is not used
+      invocation.isCommandAvailable = vi.fn(async (command: string) => {
+        if (command === 'git') return false;
+        if (command === 'grep') return true;
+        return false;
+      });
+
+      await invocation.execute({ abortSignal });
+
+      expect(execStreaming).toHaveBeenCalledWith(
+        'grep',
+        expect.arrayContaining(['-i']),
+        expect.objectContaining({
+          cwd: expect.any(String),
+        }),
+      );
+    });
+
     it('should throw an error if params are invalid', async () => {
       const params = { dir_path: '.' } as unknown as GrepToolParams; // Invalid: pattern missing
       expect(() => grepTool.build(params)).toThrow(
diff --git a/packages/core/src/tools/grep.ts b/packages/core/src/tools/grep.ts
index 34be588573..d89da94aab 100644
--- a/packages/core/src/tools/grep.ts
+++ b/packages/core/src/tools/grep.ts
@@ -465,7 +465,7 @@ class GrepToolInvocation extends BaseToolInvocation<
       const grepAvailable = await this.isCommandAvailable('grep');
       if (grepAvailable) {
         strategyUsed = 'system grep';
-        const grepArgs = ['-r', '-n', '-H', '-E', '-I'];
+        const grepArgs = ['-r', '-n', '-H', '-E', '-I', '-i'];
         // Extract directory names from exclusion patterns for grep --exclude-dir
         const globExcludes = this.fileExclusions.getGlobExcludes();
         const commonExcludes = globExcludes