diff --git a/ldm/generate.py b/ldm/generate.py
index f3ad325409..c421a52802 100644
--- a/ldm/generate.py
+++ b/ldm/generate.py
@@ -847,7 +847,7 @@ class Generate:
         # the model cache does the loading and offloading
         cache = self.model_manager
         if not cache.valid_model(model_name):
-            raise KeyError('** "{model_name}" is not a known model name. Cannot change.')
+            raise KeyError(f'** "{model_name}" is not a known model name. Cannot change.')
 
         cache.print_vram_usage()