diff --git a/src/humanize/number.py b/src/humanize/number.py
index 2ca7a69..77b79ab 100644
--- a/src/humanize/number.py
+++ b/src/humanize/number.py
@@ -261,7 +261,9 @@ def intword(value: NumberOrString, format: str = "%.1f") -> str:
 
     singular, plural = human_powers[ordinal]
     unit = _ngettext(singular, plural, math.ceil(rounded_value))
-    return f"{negative_prefix}{format % rounded_value} {unit}"
+    decimal_sep = decimal_separator()
+    number = (format % rounded_value).replace(".", decimal_sep)
+    return f"{negative_prefix}{number} {unit}"
 
 
 def apnumber(value: NumberOrString) -> str:
diff --git a/tests/test_i18n.py b/tests/test_i18n.py
index 6c16c94..319a55d 100644
--- a/tests/test_i18n.py
+++ b/tests/test_i18n.py
@@ -91,6 +91,12 @@ def test_naturaldelta() -> None:
 @pytest.mark.parametrize(
     "locale, number, expected_result",
     [
+        # Italian uses comma as decimal separator
+        ("it_IT", 1_000_000, "1,0 milione"),
+        ("it_IT", 1_200_000, "1,2 milioni"),
+        ("it_IT", 1_000_000_000, "1,0 miliardo"),
+        ("it_IT", 3_500_000_000, "3,5 miliardi"),
+        # Spanish uses dot as decimal separator
         ("es_ES", 1_000_000, "1.0 millón"),
         ("es_ES", 3_500_000, "3.5 millones"),
         ("es_ES", 1_000_000_000, "1.0 billón"),