diff --git a/src/helper.ts b/src/helper.ts
index 64ad795..d5bbeee 100644
--- a/src/helper.ts
+++ b/src/helper.ts
@@ -133,7 +133,11 @@ export const hexNumber = /^[0-9a-fA-F]+$/;
 
 export const octalNumber = /^[0-7]+$/;
 
-export const charLiteral = /^(?:\\u[0-9a-fA-F]{4}$|\\x[0-9a-fA-F]{2}|\\\d{1,3})/; // last option refers to octal character or capture group backreference
+// octal escape sequences are not matched here because they should be wrapped in a character class
+export const negatableCharLiteral = /^(?:\\u[0-9a-fA-F]{4}|\\x[0-9a-fA-F]{2})$/;
+
+// last option refers to octal character or capture group backreference
+export const charLiteral = /^(?:\\u[0-9a-fA-F]{4}|\\x[0-9a-fA-F]{2}|\\\d{1,3})$/;
 
 export const captureName = /^[a-zA-Z_][a-zA-Z0-9_]*$/;
 
diff --git a/src/modifiers/NegationModifier.ts b/src/modifiers/NegationModifier.ts
index 57727ea..8aacb83 100644
--- a/src/modifiers/NegationModifier.ts
+++ b/src/modifiers/NegationModifier.ts
@@ -1,5 +1,5 @@
 import { RegExpModifier } from '../types';
-import { charLiteral, isBracketGroup, isCharacterClass, negatableTokens } from '../helper';
+import { isBracketGroup, isCharacterClass, negatableCharLiteral, negatableTokens } from '../helper';
 
 export default class NegationModifier implements RegExpModifier {
   public modify(regExp: string): [string, string?] {
@@ -15,7 +15,7 @@ export default class NegationModifier implements RegExpModifier {
       case '$':
         return [`(?!${regExp})`];
       default:
-        if (charLiteral.test(regExp)) {
+        if (negatableCharLiteral.test(regExp)) {
           return [`[^${regExp}]`];
         } else if (negatableTokens.test(regExp)) {
           return [regExp.toUpperCase()];