diff --git a/CHANGELOG.md b/CHANGELOG.md
index 73d03dc9f1..a60c8c50f7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,9 @@
+# [Unreleased](https://github.com/pybamm-team/PyBaMM/)
+
+## Bug fixes
+
+-   Fixed `sympy` operators for `Arctan` and `Exponential` ([#1786](https://github.com/pybamm-team/PyBaMM/pull/1786))
+
 # [v21.10](https://github.com/pybamm-team/PyBaMM/tree/v21.9) - 2021-10-31
 
 ## Features
diff --git a/pybamm/expression_tree/functions.py b/pybamm/expression_tree/functions.py
index ebe2cfd356..59b05b5170 100644
--- a/pybamm/expression_tree/functions.py
+++ b/pybamm/expression_tree/functions.py
@@ -321,6 +321,10 @@ def _function_diff(self, children, idx):
         """See :meth:`pybamm.Function._function_diff()`."""
         return 1 / (children[0] ** 2 + 1)
 
+    def _sympy_operator(self, child):
+        """Override :meth:`pybamm.Function._sympy_operator`"""
+        return sympy.atan(child)
+
 
 def arctan(child):
     """Returns hyperbolic tan function of child."""
@@ -390,6 +394,10 @@ def _function_diff(self, children, idx):
         """See :meth:`pybamm.Function._function_diff()`."""
         return Exponential(children[0])
 
+    def _sympy_operator(self, child):
+        """Override :meth:`pybamm.Function._sympy_operator`"""
+        return sympy.exp(child)
+
 
 def exp(child):
     """Returns exponential function of child."""
diff --git a/tests/unit/test_expression_tree/test_functions.py b/tests/unit/test_expression_tree/test_functions.py
index ffbe514f20..5c7f5bba95 100644
--- a/tests/unit/test_expression_tree/test_functions.py
+++ b/tests/unit/test_expression_tree/test_functions.py
@@ -140,6 +140,12 @@ def test_to_equation(self):
         # Test Arcsinh
         self.assertEqual(pybamm.Arcsinh(a).to_equation(), sympy.asinh(a))
 
+        # Test Arctan
+        self.assertEqual(pybamm.Arctan(a).to_equation(), sympy.atan(a))
+
+        # Test Exponential
+        self.assertEqual(pybamm.Exponential(a).to_equation(), sympy.exp(a))
+
         # Test log
         self.assertEqual(pybamm.Log(54.0).to_equation(), sympy.log(54.0))