diff --git a/pythainlp/util/digitconv.py b/pythainlp/util/digitconv.py
index 76bee6091..c7caecc77 100644
--- a/pythainlp/util/digitconv.py
+++ b/pythainlp/util/digitconv.py
@@ -84,7 +84,7 @@ def thai_digit_to_arabic_digit(text: str) -> str:
         # output: เป็นจำนวน 123,400.25 บาท
     """
     if not text or not isinstance(text, str):
-        return ""
+        raise TypeError("The text must be str type.")
 
     return text.translate(_thai_arabic_translate_table)
 
@@ -110,7 +110,7 @@ def arabic_digit_to_thai_digit(text: str) -> str:
         # output: เป็นจำนวน ๑๒๓,๔๐๐.๒๕ บาท
     """
     if not text or not isinstance(text, str):
-        return ""
+        raise TypeError("The text must be str type.")
 
     # Convert Arabic to Thai numerals
     return text.translate(_arabic_thai_translate_table)
@@ -122,7 +122,7 @@ def digit_to_text(text: str) -> str:
     :return: Text with digits spelled out in Thai
     """
     if not text or not isinstance(text, str):
-        return ""
+        raise TypeError("The text must be str type.")
 
     # Convert Thai numerals to Arabic ones
     text = text.translate(_thai_arabic_translate_table)
@@ -161,7 +161,9 @@ def text_to_arabic_digit(text: str) -> str:
         text_to_arabic_digit("เก้าร้อย") == ""
         # output: True
     """
-    if not text or text not in _spell_digit:
+    if not isinstance(text, str):
+        raise TypeError("The text must be str type.")
+    elif not text or text not in _spell_digit:
         return ""
 
     return _spell_digit[text]
@@ -197,4 +199,9 @@ def text_to_thai_digit(text: str) -> str:
         text_to_thai_digit("เก้าร้อย") == ""
         # output: True
     """
+    if not isinstance(text, str):
+        raise TypeError("The text must be str type.")
+    elif not text:
+        return ""
+
     return arabic_digit_to_thai_digit(text_to_arabic_digit(text))
diff --git a/tests/core/test_util.py b/tests/core/test_util.py
index 73fcce8b9..9c46ad2aa 100644
--- a/tests/core/test_util.py
+++ b/tests/core/test_util.py
@@ -164,26 +164,34 @@ def test_number(self):
         self.assertEqual(
             arabic_digit_to_thai_digit("ไทยแลนด์ 4.0"), "ไทยแลนด์ ๔.๐"
         )
-        self.assertEqual(arabic_digit_to_thai_digit(""), "")
-        self.assertEqual(arabic_digit_to_thai_digit(None), "")
+        with self.assertRaises(TypeError):
+            arabic_digit_to_thai_digit("")
+        with self.assertRaises(TypeError):
+            arabic_digit_to_thai_digit(None)
 
         self.assertEqual(
             thai_digit_to_arabic_digit("๔๐๔ Not Found"), "404 Not Found"
         )
-        self.assertEqual(thai_digit_to_arabic_digit(""), "")
-        self.assertEqual(thai_digit_to_arabic_digit(None), "")
+        with self.assertRaises(TypeError):
+            thai_digit_to_arabic_digit("")
+        with self.assertRaises(TypeError):
+            thai_digit_to_arabic_digit(None)
 
         self.assertEqual(digit_to_text("RFC 7258"), "RFC เจ็ดสองห้าแปด")
-        self.assertEqual(digit_to_text(""), "")
-        self.assertEqual(digit_to_text(None), "")
+        with self.assertRaises(TypeError):
+            digit_to_text("")
+        with self.assertRaises(TypeError):
+            digit_to_text(None)
 
         self.assertEqual(text_to_arabic_digit("เจ็ด"), "7")
         self.assertEqual(text_to_arabic_digit(""), "")
-        self.assertEqual(text_to_arabic_digit(None), "")
+        with self.assertRaises(TypeError):
+            text_to_arabic_digit(None)
 
         self.assertEqual(text_to_thai_digit("เก้า"), "๙")
         self.assertEqual(text_to_thai_digit(""), "")
-        self.assertEqual(text_to_thai_digit(None), "")
+        with self.assertRaises(TypeError):
+            text_to_thai_digit(None)
 
     # ### pythainlp.util.keyboard