diff --git a/src/cac.ts b/src/cac.ts
index 7c1d219..8ddc14e 100644
--- a/src/cac.ts
+++ b/src/cac.ts
@@ -4,7 +4,7 @@ import * as fish from './fish';
 import * as powershell from './powershell';
 import type { CAC } from 'cac';
 import { Completion } from './index';
-import { CompletionConfig, noopHandler } from './shared';
+import { CompletionConfig, noopHandler, assertDoubleDashes } from './shared';
 
 const execPath = process.execPath;
 const processArgs = process.argv.slice(1);
@@ -85,7 +85,9 @@ export default async function tab(
         break;
       }
       default: {
-        const args: string[] = extra['--'];
+        assertDoubleDashes(instance.name);
+
+        const args: string[] = extra['--'] || [];
         instance.showHelpOnExit = false;
 
         // Parse current command context
diff --git a/src/citty.ts b/src/citty.ts
index e786cd1..f7affe4 100644
--- a/src/citty.ts
+++ b/src/citty.ts
@@ -11,7 +11,7 @@ import type {
   SubCommandsDef,
 } from 'citty';
 import { generateFigSpec } from './fig';
-import { CompletionConfig, noopHandler } from './shared';
+import { CompletionConfig, noopHandler, assertDoubleDashes } from './shared';
 
 function quoteIfNeeded(path: string) {
   return path.includes(' ') ? `'${path}'` : path;
@@ -155,7 +155,6 @@ export default async function tab<TArgs extends ArgsDef>(
     },
     async run(ctx) {
       let shell: string | undefined = ctx.rawArgs[0];
-      const extra = ctx.rawArgs.slice(ctx.rawArgs.indexOf('--') + 1);
 
       if (shell === '--') {
         shell = undefined;
@@ -188,6 +187,9 @@ export default async function tab<TArgs extends ArgsDef>(
           break;
         }
         default: {
+          assertDoubleDashes(name);
+
+          const extra = ctx.rawArgs.slice(ctx.rawArgs.indexOf('--') + 1);
           // const args = (await resolve(instance.args))!;
           // const parsed = parseArgs(extra, args);
           // TODO: this is not ideal at all
diff --git a/src/commander.ts b/src/commander.ts
index bcdd5d4..7a9d842 100644
--- a/src/commander.ts
+++ b/src/commander.ts
@@ -4,6 +4,7 @@ import * as fish from './fish';
 import * as powershell from './powershell';
 import type { Command as CommanderCommand } from 'commander';
 import { Completion } from './';
+import { assertDoubleDashes } from './shared';
 
 const execPath = process.execPath;
 const processArgs = process.argv.slice(1);
@@ -79,6 +80,8 @@ export default function tab(instance: CommanderCommand): Completion {
           break;
         }
         default: {
+          assertDoubleDashes(programName);
+
           // Parse current command context for autocompletion
           return completion.parse(extra);
         }
diff --git a/src/shared.ts b/src/shared.ts
index 23e4acf..798b525 100644
--- a/src/shared.ts
+++ b/src/shared.ts
@@ -16,3 +16,13 @@ export interface CompletionConfig {
     }
   >;
 }
+
+export function assertDoubleDashes(programName: string = 'cli'): void {
+  const dashDashIndex = process.argv.indexOf('--');
+
+  if (dashDashIndex === -1) {
+    const errorMessage = `Error: You need to use -- to separate completion arguments.\nExample: ${programName} complete -- <args>`;
+    console.error(errorMessage);
+    process.exit(1);
+  }
+}