diff --git a/pythainlp/transliterate/tltk.py b/pythainlp/transliterate/tltk.py
index 12da6c25c..16581b800 100644
--- a/pythainlp/transliterate/tltk.py
+++ b/pythainlp/transliterate/tltk.py
@@ -16,15 +16,21 @@ def romanize(text: str) -> str:
     :return: A string of Thai words rendered in the Latin alphabet.
     :rtype: str
     """
+    # Replace ฅ with ค to avoid KeyError in tltk (out-of-vocabulary issue)
+    text = text.replace("ฅ", "ค")
     _temp = th2roman(text)
     return _temp[: _temp.rfind(" <s/>")].replace("<s/>", "")
 
 
 def tltk_g2p(text: str) -> str:
+    # Replace ฅ with ค to avoid KeyError in tltk (out-of-vocabulary issue)
+    text = text.replace("ฅ", "ค")
     _temp = g2p(text).split("<tr/>")[1].replace("|<s/>", "").replace("|", " ")
     return _temp.replace("<s/>", "")
 
 
 def tltk_ipa(text: str) -> str:
+    # Replace ฅ with ค to avoid KeyError in tltk (out-of-vocabulary issue)
+    text = text.replace("ฅ", "ค")
     _temp = th2ipa(text)
     return _temp[: _temp.rfind(" <s/>")].replace("<s/>", "")
diff --git a/tests/extra/testx_transliterate.py b/tests/extra/testx_transliterate.py
index 231f3b510..43683f8ce 100644
--- a/tests/extra/testx_transliterate.py
+++ b/tests/extra/testx_transliterate.py
@@ -18,6 +18,8 @@
 class TransliterateTestCaseX(unittest.TestCase):
     def test_romanize(self):
         self.assertEqual(romanize("แมว", engine="tltk"), "maeo")
+        # Test for character ฅ (issue: Transliterator cannot handle ฅ)
+        self.assertIsNotNone(romanize("ภาษาไวคาลีฅ", engine="tltk"))
 
     def test_romanize_thai2rom(self):
         self.assertEqual(romanize("แมว", engine="thai2rom"), "maeo")
@@ -146,6 +148,9 @@ def test_transliterate(self):
         self.assertIsNotNone(transliterate("แมว", engine="tltk_g2p"))
         self.assertIsNotNone(transliterate("คน", engine="tltk_ipa"))
         self.assertIsNotNone(transliterate("แมว", engine="tltk_ipa"))
+        # Test for character ฅ (issue: Transliterator cannot handle ฅ)
+        self.assertIsNotNone(transliterate("ภาษาไวคาลีฅ", engine="tltk_g2p"))
+        self.assertIsNotNone(transliterate("ภาษาไวคาลีฅ", engine="tltk_ipa"))
 
         self.assertIsNotNone(trans_list("คน"))
         self.assertIsNotNone(xsampa_list("คน"))