diff --git a/interfaces/cython/cantera/ctcxx.pxd b/interfaces/cython/cantera/ctcxx.pxd
index 4ab4103ecf..28b77d7ff8 100644
--- a/interfaces/cython/cantera/ctcxx.pxd
+++ b/interfaces/cython/cantera/ctcxx.pxd
@@ -33,3 +33,4 @@ cdef extern from "<memory>":
     cppclass shared_ptr "std::shared_ptr" [T]:
         T* get()
         void reset(T*)
+        void reset()
diff --git a/interfaces/cython/cantera/reaction.pxd b/interfaces/cython/cantera/reaction.pxd
index 9770198b8e..fde60b5e39 100644
--- a/interfaces/cython/cantera/reaction.pxd
+++ b/interfaces/cython/cantera/reaction.pxd
@@ -253,7 +253,7 @@ cdef class CustomRate(ReactionRate):
     cdef Func1 _rate_func  # prevent premature garbage collection
 
 cdef class ExtensibleRate(ReactionRate):
-    pass
+    cdef set_cxx_object(self, CxxReactionRate* rate=*)
 
 cdef class InterfaceRateBase(ArrheniusRateBase):
     cdef CxxInterfaceRateBase* interface
diff --git a/interfaces/cython/cantera/reaction.pyx b/interfaces/cython/cantera/reaction.pyx
index 3151187977..04492ec073 100644
--- a/interfaces/cython/cantera/reaction.pyx
+++ b/interfaces/cython/cantera/reaction.pyx
@@ -722,8 +722,17 @@ cdef class ExtensibleRate(ReactionRate):
             self.set_cxx_object()
 
     def __init__(self, *args, **kwargs):
-        assign_delegates(self, dynamic_cast[CxxDelegatorPtr](self.rate))
-        super().__init__(*args, **kwargs)
+        if self._rate.get() is not NULL:
+            assign_delegates(self, dynamic_cast[CxxDelegatorPtr](self.rate))
+        # ReactionRate does not define __init__, so it does not need to be called
+
+    cdef set_cxx_object(self, CxxReactionRate* rate=NULL):
+        if rate is NULL:
+            self.rate = self._rate.get()
+        else:
+            self._rate.reset()
+            self.rate = rate
+            assign_delegates(self, dynamic_cast[CxxDelegatorPtr](self.rate))
 
 cdef class InterfaceRateBase(ArrheniusRateBase):
     """