diff --git a/pandas/core/reshape/merge.py b/pandas/core/reshape/merge.py
index 19e53a883d1e2..e6e84c2135b82 100644
--- a/pandas/core/reshape/merge.py
+++ b/pandas/core/reshape/merge.py
@@ -2065,8 +2065,8 @@ def _validate_left_right_on(self, left_on, right_on):
             or is_string_dtype(ro_dtype)
         ):
             raise MergeError(
-                f"Incompatible merge dtype, {ro_dtype!r} and "
-                f"{lo_dtype!r}, both sides must have numeric dtype"
+                f"Incompatible merge dtype, {lo_dtype!r} and "
+                f"{ro_dtype!r}, both sides must have numeric dtype"
             )
 
         # add 'by' to our key-list so we can have it in the