diff --git a/rdflib/plugins/serializers/trix.py b/rdflib/plugins/serializers/trix.py
index 4db436891..1ff9008f9 100644
--- a/rdflib/plugins/serializers/trix.py
+++ b/rdflib/plugins/serializers/trix.py
@@ -47,7 +47,7 @@ def serialize(
         elif isinstance(self.store, Graph):
             self._writeGraph(self.store)
         else:
-            raise Exception("Unknown graph type: " + type(self.store))
+            raise Exception(f"Unknown graph type: {type(self.store)}")
 
         self.writer.pop()
         stream.write("\n".encode("latin-1"))