diff --git a/linx/reactions.py b/linx/reactions.py
index ce2102e..e5e14cf 100644
--- a/linx/reactions.py
+++ b/linx/reactions.py
@@ -156,10 +156,10 @@ def __init__(
 
             self.frwrd_rate_param_func = frwrd_rate_param_func 
 
-        else: 
+        else:
 
-            return TypeError('Must include spline data points or analytic \
-                             function for rates.')
+            raise TypeError('Must include spline data points or analytic '
+                            'function for rates.')
 
     @eqx.filter_jit
     def frwrd_rate_param(self, T, p):