diff --git a/pandas/_libs/tslibs/timedeltas.pyx b/pandas/_libs/tslibs/timedeltas.pyx
index 1c3e69e21aa18..2862e62e3d522 100644
--- a/pandas/_libs/tslibs/timedeltas.pyx
+++ b/pandas/_libs/tslibs/timedeltas.pyx
@@ -1151,7 +1151,7 @@ class Timedelta(_Timedelta):
 
         if unit in {'Y', 'y', 'M'}:
             raise ValueError(
-                "Units 'M' and 'Y' are no longer supported, as they do not "
+                "Units 'M', 'Y', and 'y' are no longer supported, as they do not "
                 "represent unambiguous timedelta values durations."
             )
 
diff --git a/pandas/core/indexes/timedeltas.py b/pandas/core/indexes/timedeltas.py
index f6661c6b50dfb..dccc8369c5366 100644
--- a/pandas/core/indexes/timedeltas.py
+++ b/pandas/core/indexes/timedeltas.py
@@ -136,7 +136,7 @@ def __new__(
 
         if unit in {"Y", "y", "M"}:
             raise ValueError(
-                "Units 'M' and 'Y' are no longer supported, as they do not "
+                "Units 'M', 'Y', and 'y' are no longer supported, as they do not "
                 "represent unambiguous timedelta values durations."
             )
 
diff --git a/pandas/core/tools/timedeltas.py b/pandas/core/tools/timedeltas.py
index a643c312ec358..e457a8819f27a 100644
--- a/pandas/core/tools/timedeltas.py
+++ b/pandas/core/tools/timedeltas.py
@@ -94,7 +94,7 @@ def to_timedelta(arg, unit=None, errors="raise"):
 
     if unit in {"Y", "y", "M"}:
         raise ValueError(
-            "Units 'M' and 'Y' are no longer supported, as they do not "
+            "Units 'M', 'Y', and 'y' are no longer supported, as they do not "
             "represent unambiguous timedelta values durations."
         )
 
diff --git a/pandas/tests/indexes/timedeltas/test_constructors.py b/pandas/tests/indexes/timedeltas/test_constructors.py
index acc68dfe7301f..41e4e220c999c 100644
--- a/pandas/tests/indexes/timedeltas/test_constructors.py
+++ b/pandas/tests/indexes/timedeltas/test_constructors.py
@@ -12,7 +12,7 @@
 class TestTimedeltaIndex:
     @pytest.mark.parametrize("unit", ["Y", "y", "M"])
     def test_unit_m_y_raises(self, unit):
-        msg = "Units 'M' and 'Y' are no longer supported"
+        msg = "Units 'M', 'Y', and 'y' are no longer supported"
         with pytest.raises(ValueError, match=msg):
             TimedeltaIndex([1, 3, 7], unit)
 
diff --git a/pandas/tests/scalar/timedelta/test_timedelta.py b/pandas/tests/scalar/timedelta/test_timedelta.py
index 38e77321418d1..a01921bd6c4c2 100644
--- a/pandas/tests/scalar/timedelta/test_timedelta.py
+++ b/pandas/tests/scalar/timedelta/test_timedelta.py
@@ -265,7 +265,7 @@ def test_unit_parser(self, units, np_unit, wrapper):
 
     @pytest.mark.parametrize("unit", ["Y", "y", "M"])
     def test_unit_m_y_raises(self, unit):
-        msg = "Units 'M' and 'Y' are no longer supported"
+        msg = "Units 'M', 'Y', and 'y' are no longer supported"
         with pytest.raises(ValueError, match=msg):
             Timedelta(10, unit)