diff --git a/piker/clearing/_ems.py b/piker/clearing/_ems.py
index e00676f2..17f9be1a 100644
--- a/piker/clearing/_ems.py
+++ b/piker/clearing/_ems.py
@@ -80,7 +80,9 @@ def mk_check(
 
         return check_lt
 
-    raise ValueError('trigger: {trigger_price}, last: {known_last}')
+    raise ValueError(
+        f'trigger: {trigger_price}, last: {known_last}'
+    )
 
 
 @dataclass