diff --git a/src/commands/completion.test.ts b/src/commands/completion.test.ts
index 8388a09..c1bbdcf 100644
--- a/src/commands/completion.test.ts
+++ b/src/commands/completion.test.ts
@@ -23,8 +23,16 @@ describe('isShell / detectShell', () => {
     expect(detectShell({ SHELL: '/usr/local/bin/fish' })).toBe('fish');
   });
 
+  it('detects shells with Windows backslashes, .exe suffixes, and uppercase paths', () => {
+    expect(detectShell({ SHELL: 'C:\\Program Files\\Git\\bin\\bash.exe' })).toBe('bash');
+    expect(detectShell({ SHELL: 'C:\\tools\\zsh.exe' })).toBe('zsh');
+    expect(detectShell({ SHELL: '/usr/bin/FISH.EXE' })).toBe('fish');
+    expect(detectShell({ SHELL: 'C:/Program Files\\Git\\bin/bash.exe' })).toBe('bash');
+  });
+
   it('returns undefined for an unknown or missing shell', () => {
     expect(detectShell({ SHELL: '/bin/sh' })).toBeUndefined();
+    expect(detectShell({ SHELL: 'C:\\Windows\\System32\\cmd.exe' })).toBeUndefined();
     expect(detectShell({})).toBeUndefined();
   });
 });
diff --git a/src/commands/completion.ts b/src/commands/completion.ts
index 15cf7a4..42668fa 100644
--- a/src/commands/completion.ts
+++ b/src/commands/completion.ts
@@ -42,7 +42,8 @@ export function isShell(value: string): value is Shell {
 /** Best-effort shell detection from `$SHELL` (e.g. "/bin/zsh" -> "zsh"). */
 export function detectShell(env: NodeJS.ProcessEnv): Shell | undefined {
   const shellPath = env.SHELL ?? '';
-  const base = shellPath.slice(shellPath.lastIndexOf('/') + 1);
+  const rawBase = shellPath.split(/[/\\]/).pop() ?? '';
+  const base = rawBase.toLowerCase().replace(/\.exe$/, '');
   return isShell(base) ? base : undefined;
 }