diff --git a/include/cantera/thermo/Phase.h b/include/cantera/thermo/Phase.h
index 0d5d4008ae..7f5c37fd75 100644
--- a/include/cantera/thermo/Phase.h
+++ b/include/cantera/thermo/Phase.h
@@ -716,6 +716,11 @@ class Phase
     //!     @return A vector of species names for matching species.
     virtual std::vector<std::string> findIsomers(const compositionMap& compMap) const;
 
+    //! Return a vector with isomers names matching a given composition string
+    //!     @param comp String containing a composition map
+    //!     @return A vector of species names for matching species.
+    virtual std::vector<std::string> findIsomers(const std::string& comp) const;
+
     //! Return the Species object for the named species. Changes to this object
     //! do not affect the ThermoPhase object until the #modifySpecies function
     //! is called.
diff --git a/interfaces/cython/cantera/_cantera.pxd b/interfaces/cython/cantera/_cantera.pxd
index 407eddc5bf..58d8b2650a 100644
--- a/interfaces/cython/cantera/_cantera.pxd
+++ b/interfaces/cython/cantera/_cantera.pxd
@@ -185,6 +185,7 @@ cdef extern from "cantera/thermo/ThermoPhase.h" namespace "Cantera":
         void setCaseSensitiveSpecies(cbool)
         void addSpeciesAlias(string, string) except +translate_exception
         vector[string] findIsomers(Composition&) except +translate_exception
+        vector[string] findIsomers(string) except +translate_exception
 
         double molecularWeight(size_t) except +translate_exception
         double meanMolecularWeight()
diff --git a/interfaces/cython/cantera/test/test_thermo.py b/interfaces/cython/cantera/test/test_thermo.py
index 66ca27472b..fa2b50f5de 100644
--- a/interfaces/cython/cantera/test/test_thermo.py
+++ b/interfaces/cython/cantera/test/test_thermo.py
@@ -1145,6 +1145,8 @@ def test_alias(self):
         self.assertTrue(self.gas.species_index('hydrogen') == 0)
         self.gas.X = 'hydrogen:.5, O2:.5'
         self.assertNear(self.gas.X[0], 0.5)
+        with self.assertRaisesRegex(ct.CanteraError, 'Invalid alias'):
+            self.gas.add_species_alias('H2', 'O2')
         with self.assertRaisesRegex(ct.CanteraError, 'Unable to add alias'):
             self.gas.add_species_alias('spam', 'eggs')
 
@@ -1152,6 +1154,8 @@ def test_isomers(self):
         gas = ct.Solution('nDodecane_Reitz.yaml')
         iso = gas.find_isomers({'C':4, 'H':9, 'O':2})
         self.assertTrue(len(iso) == 2)
+        iso = gas.find_isomers('C:4, H:9, O:2')
+        self.assertTrue(len(iso) == 2)
         iso = gas.find_isomers({'C':7, 'H':15})
         self.assertTrue(len(iso) == 1)
         iso = gas.find_isomers({'C':7, 'H':16})
diff --git a/interfaces/cython/cantera/thermo.pyx b/interfaces/cython/cantera/thermo.pyx
index 7d333e2944..01defe4e97 100644
--- a/interfaces/cython/cantera/thermo.pyx
+++ b/interfaces/cython/cantera/thermo.pyx
@@ -535,8 +535,12 @@ cdef class ThermoPhase(_SolutionBase):
         Find species/isomers matching a composition specified by *comp*.
         """
 
-        assert isinstance(comp, dict), 'Composition needs to be specified as dictionary'
-        iso = self.thermo.findIsomers(comp_map(comp))
+        if isinstance(comp, dict):
+            iso = self.thermo.findIsomers(comp_map(comp))
+        elif isinstance(comp, (str, bytes)):
+            iso = self.thermo.findIsomers(stringify(comp))
+        else:
+            raise CanteraError('Invalid composition')
 
         return [pystr(b) for b in iso]
 
diff --git a/src/thermo/Phase.cpp b/src/thermo/Phase.cpp
index af50f1634b..c0fd0e1bb7 100644
--- a/src/thermo/Phase.cpp
+++ b/src/thermo/Phase.cpp
@@ -881,6 +881,11 @@ vector<std::string> Phase::findIsomers(const compositionMap& compMap) const
     return isomerNames;
 }
 
+vector<std::string> Phase::findIsomers(const std::string& comp) const
+{
+    return findIsomers(parseCompString(comp));
+}
+
 shared_ptr<Species> Phase::species(const std::string& name) const
 {
     size_t k = speciesIndex(name);