diff --git a/spec/match-char-class.spec.js b/spec/match-char-class.spec.js
index 7c0cac7..4e606ae 100644
--- a/spec/match-char-class.spec.js
+++ b/spec/match-char-class.spec.js
@@ -38,7 +38,12 @@ describe('CharacterClass', () => {
         expect('\u{1}').toExactlyMatch(r`[\01]`);
         expect('\u{1}').toExactlyMatch(r`[\001]`);
         expect(cp(0o17)).toExactlyMatch(r`[\17]`);
-        expect(cp(0o777)).toExactlyMatch(r`[\777]`);
+        expect(cp(0o177)).toExactlyMatch(r`[\177]`);
+      });
+
+      it(r`should throw for UTF-8 encoded byte sequence in octal (above \177)`, () => {
+        expect(() => toDetails(r`[\200]`)).toThrow();
+        expect(() => toDetails(r`[\777]`)).toThrow();
       });
 
       it('should match octals followed by literal digits', () => {
diff --git a/spec/match-char.spec.js b/spec/match-char.spec.js
index b769a15..386d188 100644
--- a/spec/match-char.spec.js
+++ b/spec/match-char.spec.js
@@ -133,7 +133,12 @@ describe('Character', () => {
       expect('\u{1}').toExactlyMatch(r`\01`);
       expect('\u{1}').toExactlyMatch(r`\001`);
       expect(cp(0o17)).toExactlyMatch(r`\17`);
-      expect(cp(0o777)).toExactlyMatch(r`\777`);
+      expect(cp(0o177)).toExactlyMatch(r`\177`);
+    });
+
+    it(r`should throw for UTF-8 encoded byte sequence in octal (above \177)`, () => {
+      expect(() => toDetails(r`\200`)).toThrow();
+      expect(() => toDetails(r`\777`)).toThrow();
     });
 
     it('should match octals followed by literal digits', () => {
diff --git a/src/tokenize.js b/src/tokenize.js
index 1291bd6..8cd019f 100644
--- a/src/tokenize.js
+++ b/src/tokenize.js
@@ -676,9 +676,8 @@ function getValidatedHexCharCode(raw) {
     /^\\x\{\s*(?<hex>\p{AHex}+)/u.exec(raw).groups.hex :
     raw.slice(2);
   const dec = parseInt(hex, 16);
-  if (dec > 0x7F && /^\\x\p{AHex}/u.test(raw)) {
-    throw new Error(r`\xNN above 7F unsupported in Oniguruma "${raw}"`);
-  } else if (dec > 0x13FFFF) {
+  // `\xNN` above 0x7F is handled elsewhere as a UTF-8 encoded byte sequence
+  if (dec > 0x13FFFF) {
     throw new Error(`Invalid out of range "${raw}"`);
   } else if (dec > 0x10FFFF) {
     throw new Error(`Invalid out of range in JS "${raw}"`);
@@ -708,10 +707,17 @@ function splitEscapedNumToken(token, numCaptures) {
   const matches = value.match(/^[0-7]+|\d/g);
   for (let i = 0; i < matches.length; i++) {
     const m = matches[i];
+    let value;
     // Octal digits are 0-7
-    const value = (i === 0 && m !== '8' && m !== '9') ?
-      parseInt(m, 8) :
-      m.codePointAt(0);
+    if (i === 0 && m !== '8' && m !== '9') {
+      value = parseInt(m, 8);
+      if (value > 0o177) {
+        // UTF-8 encoded byte sequence in octal; unsupported
+        throw new Error(r`Octal encoded byte above 177 unsupported "${raw}"`);
+      }
+    } else {
+      value = m.codePointAt(0);
+    }
     tokens.push(createToken(TokenTypes.Character, (i === 0 ? '\\' : '') + m, {
       value,
     }));