diff --git a/packages/@ember/-internals/glimmer/lib/helpers/fn.ts b/packages/@ember/-internals/glimmer/lib/helpers/fn.ts
index 34f28fabc7a..36ed5dec393 100644
--- a/packages/@ember/-internals/glimmer/lib/helpers/fn.ts
+++ b/packages/@ember/-internals/glimmer/lib/helpers/fn.ts
@@ -85,9 +85,8 @@ function fn({ positional }: CapturedArguments) {
   if (DEBUG && typeof callbackRef[INVOKE] !== 'function') {
     let callback = callbackRef.value();
 
-    const debug = (<any>callbackRef).debug && (<any>callbackRef).debug();
     assert(
-      `You must pass a function as the \`fn\` helpers first argument, you passed ${debug} to \`fn\` but it was ${callback}`,
+      `You must pass a function as the \`fn\` helpers first argument, you passed ${callback}`,
       typeof callback === 'function'
     );
   }
diff --git a/packages/@ember/-internals/glimmer/lib/modifiers/on.ts b/packages/@ember/-internals/glimmer/lib/modifiers/on.ts
index 5ccf9121198..2c126cea48b 100644
--- a/packages/@ember/-internals/glimmer/lib/modifiers/on.ts
+++ b/packages/@ember/-internals/glimmer/lib/modifiers/on.ts
@@ -100,15 +100,11 @@ export class OnModifierState {
       this.eventName = eventName;
       this.shouldUpdate = true;
     }
-    if (DEBUG) {
-      const debug = args.positional.at(1) && (<any>args.positional.at(1)).debug();
-      const value = args.positional.at(1) && args.positional.at(1).value();
-      assert(
-        `You must pass a function as the second argument to the \`on\` modifier, you passed ${debug} to \`on\` but it was ${value}`,
-        value !== undefined && typeof value === 'function'
-      );
-    }
 
+    assert(
+      'You must pass a function as the second argument to the `on` modifier',
+      args.positional.at(1) !== undefined && typeof args.positional.at(1).value() === 'function'
+    );
     let userProvidedCallback = args.positional.at(1).value() as EventListener;
     if (userProvidedCallback !== this.userProvidedCallback) {
       this.userProvidedCallback = userProvidedCallback;
diff --git a/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js b/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
index 2a12e852a85..24a3e7581ff 100644
--- a/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
+++ b/packages/@ember/-internals/glimmer/tests/integration/helpers/fn-test.js
@@ -127,7 +127,7 @@ moduleFor(
           arg1: 'foo',
           arg2: 'bar',
         });
-      }, /You must pass a function as the `fn` helpers first argument, you passed this.myFunc to `fn` but it was null/);
+      }, /You must pass a function as the `fn` helpers first argument, you passed null/);
     }
 
     '@test asserts if the provided function accesses `this` without being bound prior to passing to fn'(