diff --git a/src/marshmallow/fields.py b/src/marshmallow/fields.py
index dc476abf2..e02ebb075 100644
--- a/src/marshmallow/fields.py
+++ b/src/marshmallow/fields.py
@@ -1497,7 +1497,9 @@ def __init__(
         precision = precision.lower()
 
         if precision not in self._unit_to_microseconds_mapping:
-            units = ", ".join(f'"{each}"' for each in self._unit_to_microseconds_mapping)
+            units = ", ".join(
+                f'"{each}"' for each in self._unit_to_microseconds_mapping
+            )
             msg = f"The precision must be one of {units}."
             raise ValueError(msg)