diff --git a/qsymm/kwant_continuum.py b/qsymm/kwant_continuum.py
index c2e5695e4368bf838f4af8b4c57944831fdefdde..7d16e30635c8114d281f85d89a37b259a63c84cc 100644
--- a/qsymm/kwant_continuum.py
+++ b/qsymm/kwant_continuum.py
@@ -51,6 +51,7 @@ import warnings
 
 momentum_operators = sympy.symbols('k_x k_y k_z', commutative=False)
 position_operators = sympy.symbols('x y z', commutative=False)
+e = sympy.symbols('e', positive=True)
 
 pauli = [sympy.eye(2), _msigma(1), _msigma(2), _msigma(3)]
 
@@ -217,6 +218,8 @@ def sympify(expr, locals=None):
         # sympify we are getting list of sympy objects, so we call sympify
         # second time to obtain ``sympy`` matrices.
         hamiltonian = sympy.sympify(hamiltonian)
+        # A workaround for qsymm issue #48
+        hamiltonian = hamiltonian.subs(sympy.sympify('e'), e)
     finally:
         if stored_value is not None:
             converter[list] = stored_value
diff --git a/qsymm/model.py b/qsymm/model.py
index 63b14587df641f2bf7d5faff378907dd08a410c3..1cbcf49bc76178f6d580e2103aab04f33ae53bc7 100644
--- a/qsymm/model.py
+++ b/qsymm/model.py
@@ -19,8 +19,8 @@ from . import kwant_continuum
 _commutative_momenta = [kwant_continuum.make_commutative(k, k)
            for k in kwant_continuum.momentum_operators]
 
-e = kwant_continuum.sympify('e')
-I = kwant_continuum.sympify('I')  # noqa: E741
+e = kwant_continuum.e
+I = sympy.I  # noqa: E741
 
 
 def substitute_exponents(expr):
@@ -990,7 +990,7 @@ def _find_momenta(momenta):
 
 @lru_cache(maxsize=1000)
 def _symbol_normalizer(key):
-    return sympy.expand_power_exp(sympy.sympify(key))
+    return sympy.expand_power_exp(sympy.sympify(key, locals={'e': e}))
 
 
 @lru_cache(maxsize=1000)