diff --git a/lib/internal/util/comparisons.js b/lib/internal/util/comparisons.js
index 917de00918e028..ed320995b83272 100644
--- a/lib/internal/util/comparisons.js
+++ b/lib/internal/util/comparisons.js
@@ -23,6 +23,7 @@ const {
 } = primordials;
 
 const { compare } = internalBinding('buffer');
+const assert = require('internal/assert');
 const types = require('internal/util/types');
 const {
   isAnyArrayBuffer,
@@ -118,7 +119,8 @@ function isEqualBoxedPrimitive(val1, val2) {
     return isSymbolObject(val2) &&
           SymbolPrototypeValueOf(val1) === SymbolPrototypeValueOf(val2);
   }
-  return false;
+  /* c8 ignore next */
+  assert.fail(`Unknown boxed type ${val1}`);
 }
 
 function isIdenticalTypedArrayType(a, b) {