diff --git a/interfaces/cython/cantera/composite.py b/interfaces/cython/cantera/composite.py
index ef51a0896d..4b45962599 100644
--- a/interfaces/cython/cantera/composite.py
+++ b/interfaces/cython/cantera/composite.py
@@ -232,7 +232,7 @@ def __init__(self, phase, mass=None, moles=None, constant='UV'):
 
         if constant not in ('TP','TV','HP','SP','SV','UV'):
             raise ValueError(
-                f"Constant {constant} is invalid."
+                f"Constant {constant} is invalid. "
                 "Must be one of 'TP','TV','HP','SP','SV', or 'UV'")
         self.constant = constant