diff --git a/rmgpy/kinetics/arrhenius.pyx b/rmgpy/kinetics/arrhenius.pyx
index 94f7cf2846b..76694a64ade 100644
--- a/rmgpy/kinetics/arrhenius.pyx
+++ b/rmgpy/kinetics/arrhenius.pyx
@@ -689,7 +689,7 @@ cdef class ArrheniusBM(KineticsModel):
         # fill in parameters
         A_units = ['', 's^-1', 'm^3/(mol*s)', 'm^6/(mol^2*s)']
         order = len(rxns[0].reactants)
-        if order != 1 and rxn.is_surface_reaction:
+        if order != 1 and rxn.is_surface_reaction():
             raise NotImplementedError("Units not implemented for surface reactions.")
         self.A = (A, A_units[order])
 
@@ -1626,7 +1626,7 @@ cdef class ArrheniusChargeTransferBM(KineticsModel):
         # fill in parameters
         A_units = ['', 's^-1', 'm^3/(mol*s)', 'm^6/(mol^2*s)']
         order = len(rxns[0].reactants)
-        if order != 1 and rxn.is_surface_reaction:
+        if order != 1 and rxn.is_surface_reaction():
             raise NotImplementedError("Units not implemented for surface reactions")
         self.A = (A, A_units[order])