diff --git a/interfaces/cython/cantera/_cantera.pxd b/interfaces/cython/cantera/_cantera.pxd
index 78d83b15e..7d665ad0f 100644
--- a/interfaces/cython/cantera/_cantera.pxd
+++ b/interfaces/cython/cantera/_cantera.pxd
@@ -977,7 +977,7 @@ cdef class ReactionPathDiagram:
     cdef CxxStringStream* _log
 
 # free functions
-cdef string stringify(x)
+cdef string stringify(x) except *
 cdef pystr(string x)
 cdef np.ndarray get_species_array(Kinetics kin, kineticsMethod1d method)
 cdef np.ndarray get_reaction_array(Kinetics kin, kineticsMethod1d method)
diff --git a/interfaces/cython/cantera/utils.pyx b/interfaces/cython/cantera/utils.pyx
index 23b3788a3..906aa19c5 100644
--- a/interfaces/cython/cantera/utils.pyx
+++ b/interfaces/cython/cantera/utils.pyx
@@ -4,7 +4,7 @@ cdef int _pythonMajorVersion = sys.version_info[0]
 cdef CxxPythonLogger* _logger = new CxxPythonLogger()
 CxxSetLogger(_logger)
 
-cdef string stringify(x):
+cdef string stringify(x) except *:
     """ Converts Python strings to std::string. """
     # This method works with both Python 2.x and 3.x.
     if isinstance(x, bytes):