diff --git a/e3sm_diags/driver/lat_lon_driver.py b/e3sm_diags/driver/lat_lon_driver.py
index 6a2d146c6..e08bfbd45 100755
--- a/e3sm_diags/driver/lat_lon_driver.py
+++ b/e3sm_diags/driver/lat_lon_driver.py
@@ -25,7 +25,9 @@
 # type of metrics and the value is a sub-dictionary of metrics (key is metrics
 # type and value is float). There is also a "unit" key representing the
 # units for the variable.
-MetricsDict = Dict[str, str | Dict[str, float | None | List[float]]]
+UnitAttr = str
+MetricsSubDict = Dict[str, Union[float, None, List[float]]]
+MetricsDict = Dict[str, Union[UnitAttr, MetricsSubDict]]
 
 if TYPE_CHECKING:
     from e3sm_diags.parameter.core_parameter import CoreParameter