diff --git a/rmgpy/molecule/symmetry.py b/rmgpy/molecule/symmetry.py
index 5f5c40dca5..fc2180d3e1 100644
--- a/rmgpy/molecule/symmetry.py
+++ b/rmgpy/molecule/symmetry.py
@@ -99,6 +99,9 @@ def calculateAtomSymmetryNumber(molecule, atom):
         elif double == 2:
             # Two double bonds
             if count == [2]: symmetryNumber *= 2
+        # for nitrogen resonance hybrids
+        elif single == 0:
+            if count == [2]: symmetryNumber *=2
     elif atom.radicalElectrons == 1:
         if single == 3:
             # Three single bonds
@@ -111,11 +114,6 @@ def calculateAtomSymmetryNumber(molecule, atom):
             if count == [2]:
                 symmetryNumber *= 2
     
-    if atom.isNitrogen():
-        for groupN in groups:
-            if groupN.toSMILES() == "[N+](=O)[O-]":
-                symmetryNumber *= 2
-    
     return symmetryNumber
 
 ################################################################################
diff --git a/rmgpy/species.py b/rmgpy/species.py
index 985d3f5ea8..c627b38ee1 100644
--- a/rmgpy/species.py
+++ b/rmgpy/species.py
@@ -403,7 +403,14 @@ def getSymmetryNumber(self):
         if self.symmetryNumber < 1:
             cython.declare(resonanceHybrid = Molecule, maxSymmetryNum = cython.short)
             resonanceHybrid = self.getResonanceHybrid()
-            self.symmetryNumber = resonanceHybrid.getSymmetryNumber()
+            try:
+                self.symmetryNumber = resonanceHybrid.getSymmetryNumber()
+            except KeyError:
+                logging.error('Wrong bond order generated by resonance hybrid.')
+                logging.error('Resonance Hybrid: {}'.format(resonanceHybrid.toAdjacencyList()))
+                for index, mol in enumerate(self.molecule):
+                    logging.error("Resonance Structure {}: {}".format(index,mol.toAdjacencyList()))
+                raise
         return self.symmetryNumber
         
     def getResonanceHybrid(self):