diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index 7c046bddab4e8..a271d68d8f57e 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -1623,7 +1623,7 @@ def get_join_indexers(
     """
     assert len(left_keys) == len(
         right_keys
-    ), "left_key and right_keys must be the same length"
+    ), "left_keys and right_keys must be the same length"
 
     # fast-path for empty left/right
     left_n = len(left_keys[0])
@@ -1960,7 +1960,7 @@ def _validate_left_right_on(self, left_on, right_on):
                 self.right_by = [self.right_by]
 
             if len(self.left_by) != len(self.right_by):
-                raise MergeError("left_by and right_by must be same length")
+                raise MergeError("left_by and right_by must be the same length")
 
             left_on = self.left_by + list(left_on)
             right_on = self.right_by + list(right_on)
diff --git a/pandas/tests/reshape/merge/test_merge_asof.py b/pandas/tests/reshape/merge/test_merge_asof.py
index 0aa9026cc0808..2f0861201155b 100644
--- a/pandas/tests/reshape/merge/test_merge_asof.py
+++ b/pandas/tests/reshape/merge/test_merge_asof.py
@@ -455,7 +455,7 @@ def test_multiby_indexed(self):
         tm.assert_frame_equal(expected, result)
 
         with pytest.raises(
-            MergeError, match="left_by and right_by must be same length"
+            MergeError, match="left_by and right_by must be the same length"
         ):
             merge_asof(
                 left,