diff --git a/num2words/lang_CA.py b/num2words/lang_CA.py
index 97d0f29e..a386ac73 100644
--- a/num2words/lang_CA.py
+++ b/num2words/lang_CA.py
@@ -463,13 +463,16 @@ def to_currency(self, val, currency="EUR", cents=True,
         list_result[0] = list_result[0].replace(" i un", "-un")
         list_result[0] = list_result[0].replace("un", "un")
 
-        if currency in CENTS_UNA:
-            list_result[1] = list_result[1].replace("un", "una")
-            list_result[1] = list_result[1].replace("dos", "dues")
+        # The base to_currency() omits the cents part for whole amounts
+        # (e.g. integer inputs with no cents), so it may be absent here.
+        if len(list_result) > 1:
+            if currency in CENTS_UNA:
+                list_result[1] = list_result[1].replace("un", "una")
+                list_result[1] = list_result[1].replace("dos", "dues")
 
-        list_result[1] = list_result[1].replace("vint-i-un", "vint-i-una")
+            list_result[1] = list_result[1].replace("vint-i-un", "vint-i-una")
 
-        list_result[1] = list_result[1].replace("un", "un")
+            list_result[1] = list_result[1].replace("un", "un")
 
         result = (separator + " ").join(list_result)
 
diff --git a/num2words/lang_ES.py b/num2words/lang_ES.py
index ce1c9f8b..915fef58 100644
--- a/num2words/lang_ES.py
+++ b/num2words/lang_ES.py
@@ -397,18 +397,23 @@ def to_currency(self, val, currency='EUR', cents=True, separator=' con',
 
         # "CENTS" PART (list_result[1])
 
-        # Feminine "cents" ("una piastra", "veintiuna piastras"...)
-        if currency in CENTS_UNA:
+        # The base to_currency() omits the cents part for whole amounts
+        # (e.g. integer inputs with no cents), so it may be absent here.
+        if len(list_result) > 1:
 
-            # "una piastra", "veintiuna piastras", "treinta y una piastras"...
-            list_result[1] = list_result[1].replace("uno", "una")
+            # Feminine "cents" ("una piastra", "veintiuna piastras"...)
+            if currency in CENTS_UNA:
 
-        # Masc.: Correct orthography for the specific case of "veintiún":
-        list_result[1] = list_result[1].replace("veintiuno", "veintiún")
+                # "una piastra", "veintiuna piastras", "treinta y una
+                # piastras"...
+                list_result[1] = list_result[1].replace("uno", "una")
+
+            # Masc.: Correct orthography for the specific case of "veintiún":
+            list_result[1] = list_result[1].replace("veintiuno", "veintiún")
 
-        # Masculine "cents": general case ("un centavo", "treinta y un
-        # centavos"...):
-        list_result[1] = list_result[1].replace("uno", "un")
+            # Masculine "cents": general case ("un centavo", "treinta y un
+            # centavos"...):
+            list_result[1] = list_result[1].replace("uno", "un")
 
         # join back "dollars" part with "cents" part
         result = (separator + " ").join(list_result)
diff --git a/tests/test_ca.py b/tests/test_ca.py
index ab5be158..4ac8cb99 100644
--- a/tests/test_ca.py
+++ b/tests/test_ca.py
@@ -173,6 +173,20 @@ def test_ordinal_num(self):
     def test_currency(self):
         self._test_cases(TEST_CASES_TO_CURRENCY, to="currency", currency="EUR")
 
+    def test_currency_integer_whole_units(self):
+        # Regression: integer inputs are whole currency units with no cents,
+        # so the base to_currency() omits the cents segment. The CA override
+        # used to assume that segment always existed and raised IndexError.
+        cases = (
+            (0, 'zero euros'),
+            (100, 'un euro'),
+            (200, 'dos euros'),
+        )
+        for value, expected in cases:
+            self.assertEqual(
+                num2words(value, lang='ca', to='currency'), expected
+            )
+
     def test_currency_esp(self):
         self._test_cases(TEST_CASES_TO_CURRENCY_ESP,
                          to="currency", currency="ESP")
diff --git a/tests/test_es.py b/tests/test_es.py
index ce2bb033..4005ff93 100644
--- a/tests/test_es.py
+++ b/tests/test_es.py
@@ -1866,6 +1866,32 @@ def test_currency(self):
                 test[1]
             )
 
+    def test_currency_integer_whole_units(self):
+        # Regression: integer inputs resolve to whole currency units with no
+        # cents, so the base to_currency() omits the cents segment. The ES
+        # override used to assume that segment always existed and raised
+        # IndexError. See whole-unit amounts below.
+        cases = (
+            (0, 'cero euros'),
+            (100, 'un euro'),
+            (200, 'dos euros'),
+            (2100, 'veintiún euros'),
+            (12300, 'ciento veintitrés euros'),
+        )
+        for value, expected in cases:
+            self.assertEqual(
+                num2words(value, lang='es', to='currency'), expected
+            )
+        # Feminine currency keeps its grammar on the whole-unit path.
+        self.assertEqual(
+            num2words(100, lang='es', to='currency', currency='GBP'),
+            'una libra'
+        )
+        self.assertEqual(
+            num2words(2100, lang='es', to='currency', currency='GBP'),
+            'veintiuna libras'
+        )
+
     def test_currency_esp(self):
         for test in TEST_CASES_TO_CURRENCY_ESP:
             self.assertEqual(