diff --git a/src/core/prism.ts b/src/core/prism.ts
index d370c3e7f..940f3b89c 100644
--- a/src/core/prism.ts
+++ b/src/core/prism.ts
@@ -7,7 +7,7 @@ import { LinkedList } from './linked-list';
 import { Registry } from './registry';
 import { Token } from './token';
 import type { KnownPlugins } from '../known-plugins';
-import type { Grammar, GrammarToken, GrammarTokens } from '../types';
+import type { Grammar, GrammarToken, GrammarTokens, RegExpLike } from '../types';
 import type { HookEnvMap } from './hooks';
 import type { LinkedListHeadNode, LinkedListMiddleNode, LinkedListTailNode } from './linked-list';
 import type { TokenStream } from './token';
@@ -481,8 +481,8 @@ function stringify(o: string | Token | TokenStream, language: string, hooks: Hoo
 	return '<' + env.tag + ' class="' + env.classes.join(' ') + '"' + attributes + '>' + env.content + '</' + env.tag + '>';
 }
 
-function toGrammarToken(pattern: GrammarToken | RegExp): GrammarToken {
-	if (pattern.exec) {
+function toGrammarToken(pattern: GrammarToken | RegExpLike): GrammarToken {
+	if (!pattern.pattern) {
 		return { pattern };
 	} else {
 		return pattern;
diff --git a/src/shared/language-util.ts b/src/shared/language-util.ts
index 6078ab570..be3ccc43c 100644
--- a/src/shared/language-util.ts
+++ b/src/shared/language-util.ts
@@ -1,5 +1,5 @@
 import { rest, tokenize } from './symbols';
-import type { Grammar, GrammarToken, GrammarTokens } from '../types';
+import type { Grammar, GrammarToken, GrammarTokens, RegExpLike } from '../types';
 
 // TODO: Update documentation
 
@@ -119,8 +119,8 @@ function cloneGrammar(grammar: Grammar, id: string): Grammar {
 
 	const visited = new Map<Grammar, Grammar>();
 
-	function cloneToken(value: GrammarToken | RegExp) {
-		if (value.exec) {
+	function cloneToken(value: GrammarToken | RegExpLike) {
+		if (!value.pattern) {
 			return value;
 		} else {
 			const copy: GrammarToken = { pattern: value.pattern };
diff --git a/src/types.d.ts b/src/types.d.ts
index 09fb6f89b..ded966f3b 100644
--- a/src/types.d.ts
+++ b/src/types.d.ts
@@ -62,6 +62,8 @@ export type StandardTokenName =
 
 export type TokenName = string & {} | StandardTokenName;
 
+export type RegExpLike = RegExp & { readonly pattern?: never; };
+
 /**
  * The expansion of a simple `RegExp` literal to support additional properties.
  */
@@ -69,7 +71,7 @@ export interface GrammarToken {
 	/**
 	 * The regular expression of the token.
 	 */
-	pattern: RegExp
+	pattern: RegExpLike
 	/**
 	 * If `true`, then the first capturing group of `pattern` will (effectively) behave as a lookbehind group meaning that the captured text will not be part of the matched text of the new token.
 	 *
@@ -97,16 +99,9 @@ export interface GrammarToken {
 	 * each another.
 	 */
 	inside?: string | Grammar | null
-	/**
-	 * A property to make the types {@link GrammarToken} and {@link RegExp} non-overlapping.
-	 *
-	 * Since {@link GrammarToken} requires `exec` to be `undefined` and {@link RegExp} requires it to be a function,
-	 * there can be no object that is both a {@link GrammarToken} and a {@link RegExp}.
-	 */
-	readonly exec?: never;
 }
 
-export type GrammarTokens = Partial<Record<TokenName, RegExp | GrammarToken | (RegExp | GrammarToken)[]>>;
+export type GrammarTokens = Partial<Record<TokenName, RegExpLike | GrammarToken | (RegExpLike | GrammarToken)[]>>;
 export interface GrammarSymbols {
 	/**
 	 * An optional grammar object that will be appended to this grammar.