diff --git a/src/tespy/networks/network.py b/src/tespy/networks/network.py
index 2968a669..3f4580a3 100644
--- a/src/tespy/networks/network.py
+++ b/src/tespy/networks/network.py
@@ -1111,7 +1111,7 @@ def presolve_fluid_topology(self):
                 main_conn.fluid.is_var = variable
                 num_var = len(variable)
                 for f in variable:
-                    main_conn.fluid.val[f]: (1 - mass_fraction_sum) / num_var
+                    main_conn.fluid.val[f] = (1 - mass_fraction_sum) / num_var
 
             [c.build_fluid_data() for c in all_connections]
             for fluid in main_conn.fluid.is_var: