diff --git a/interfaces/cython/cantera/_cantera.pxd b/interfaces/cython/cantera/_cantera.pxd
index 22fdf7d67..815a0486e 100644
--- a/interfaces/cython/cantera/_cantera.pxd
+++ b/interfaces/cython/cantera/_cantera.pxd
@@ -1052,9 +1052,9 @@ cdef class Sim1D:
     cdef object _initialized
     cdef object _initial_guess_args
     cdef object _initial_guess_kwargs
-    cdef Func1 interrupt
-    cdef Func1 time_step_callback
-    cdef Func1 steady_callback
+    cdef public Func1 _interrupt
+    cdef public Func1 _time_step_callback
+    cdef public Func1 _steady_callback
 
 cdef class ReactionPathDiagram:
     cdef CxxReactionPathDiagram diagram
diff --git a/interfaces/cython/cantera/onedim.pyx b/interfaces/cython/cantera/onedim.pyx
index fcc9294b8..cbed3cdf2 100644
--- a/interfaces/cython/cantera/onedim.pyx
+++ b/interfaces/cython/cantera/onedim.pyx
@@ -585,8 +585,8 @@ cdef class Sim1D:
         """
         if not isinstance(f, Func1):
             f = Func1(f)
-        self.interrupt = f
-        self.sim.setInterrupt(self.interrupt.func)
+        self._interrupt = f
+        self.sim.setInterrupt(self._interrupt.func)
 
     def set_time_step_callback(self, f):
         """
@@ -596,8 +596,8 @@ cdef class Sim1D:
         """
         if not isinstance(f, Func1):
             f = Func1(f)
-        self.time_step_callback = f
-        self.sim.setTimeStepCallback(self.time_step_callback.func)
+        self._time_step_callback = f
+        self.sim.setTimeStepCallback(self._time_step_callback.func)
 
     def set_steady_callback(self, f):
         """
@@ -607,8 +607,8 @@ cdef class Sim1D:
         """
         if not isinstance(f, Func1):
             f = Func1(f)
-        self.steady_callback = f
-        self.sim.setSteadyCallback(self.steady_callback.func)
+        self._steady_callback = f
+        self.sim.setSteadyCallback(self._steady_callback.func)
 
     def domain_index(self, dom):
         """