diff --git a/num2words/lang_PL.py b/num2words/lang_PL.py
index 376b0a10..fb4e8289 100644
--- a/num2words/lang_PL.py
+++ b/num2words/lang_PL.py
@@ -221,6 +221,10 @@ def last_fragment_to_ordinal(self, last, words, level):
     def to_ordinal(self, number):
         if number % 1 != 0:
             raise NotImplementedError()
+        if number == 0:
+            # splitbyx("0") yields a single zero fragment; the loop below would
+            # pop it and then index an empty list, so handle zero explicitly.
+            return "zerowy"
         words = []
         fragments = list(splitbyx(str(number), 3))
         level = 0
diff --git a/num2words/lang_UK.py b/num2words/lang_UK.py
index 188d7ced..6b6e7977 100644
--- a/num2words/lang_UK.py
+++ b/num2words/lang_UK.py
@@ -1043,6 +1043,11 @@ def last_fragment_to_ordinal(last, words, level):
     def to_ordinal(self, number):
         self.verify_ordinal(number)
 
+        if number == 0:
+            # splitbyx("0") yields a single zero fragment; the loop below would
+            # pop it and then index an empty list, so handle zero explicitly.
+            return "нульовий"
+
         words = []
         fragments = list(splitbyx(str(number), 3))
         level = 0
diff --git a/tests/test_pl.py b/tests/test_pl.py
index 08ef0394..beb77ffc 100644
--- a/tests/test_pl.py
+++ b/tests/test_pl.py
@@ -93,6 +93,7 @@ def test_cardinal(self):
         )
 
     def test_to_ordinal(self):
+        self.assertEqual(num2words(0, lang='pl', to='ordinal'), "zerowy")
         self.assertEqual(num2words(100, lang='pl', to='ordinal'), "setny")
         self.assertEqual(
             num2words(101, lang='pl', to='ordinal'), "sto pierwszy")
diff --git a/tests/test_uk.py b/tests/test_uk.py
index 4dcd7cb1..5568a91f 100644
--- a/tests/test_uk.py
+++ b/tests/test_uk.py
@@ -700,6 +700,7 @@
 )
 
 TEST_CASES_ORDINAL = (
+    (0, "нульовий"),
     (1, "перший"),
     (2, "другий"),
     (3, "третій"),