diff --git a/pybamm/solvers/base_solver.py b/pybamm/solvers/base_solver.py
index 2038c59649..38e53903c7 100644
--- a/pybamm/solvers/base_solver.py
+++ b/pybamm/solvers/base_solver.py
@@ -8,6 +8,7 @@
 from scipy import optimize
 from scipy.sparse import issparse
 import sys
+import itertools
 
 
 class BaseSolver(object):
@@ -215,7 +216,8 @@ def report(string):
         # Check for heaviside functions in rhs and algebraic and add discontinuity
         # events if these exist.
         # Note: only checks for the case of t < X, t <= X, X < t, or X <= t
-        for symbol in model.concatenated_rhs.pre_order():
+        for symbol in itertools.chain(model.concatenated_rhs.pre_order(),
+                                      model.concatenated_algebraic.pre_order()):
             if isinstance(symbol, pybamm.Heaviside):
                 if symbol.right.id == pybamm.t.id:
                     expr = symbol.left