diff --git a/test/test_check_arities.py b/test/test_check_arities.py
index e2c32f5f5..5508c02b1 100755
--- a/test/test_check_arities.py
+++ b/test/test_check_arities.py
@@ -9,7 +9,9 @@
     TestFunction,
     TrialFunction,
     adjoint,
+    as_tensor,
     cofac,
+    conditional,
     conj,
     derivative,
     ds,
@@ -84,3 +86,41 @@ def test_product_arity():
     with pytest.raises(ArityMismatch):
         L = inner(v, v) * dx
         compute_form_data(L, complex_mode=False)
+
+
+def test_zero_simplify_arity():
+    """
+    Test that adding verious zero-like expressions to a form is simplified,
+    such that one can compute form data for the integral.
+    """
+    cell = tetrahedron
+    D = Mesh(FiniteElement("Lagrange", cell, 1, (3,), identity_pullback, H1))
+    V = FunctionSpace(D, FiniteElement("Lagrange", cell, 2, (), identity_pullback, H1))
+    v = TestFunction(V)
+    u = Coefficient(V)
+
+    nonzero = 1
+    with pytest.raises(ArityMismatch):
+        F = inner(u, v + nonzero) * dx
+        compute_form_data(F)
+    z = Coefficient(V)
+
+    # Add a Zero-component (rank-0) of a tensor to a rank-1 tensor
+    zero = as_tensor([0, z])[0]
+    F = inner(u, v + zero) * dx
+    fd = compute_form_data(F)
+    assert fd.num_coefficients == 1
+
+    # Add a conditional that should have been simplified to zero (rank-0)
+    # to a rank-1 tensor
+    zero = conditional(z < 0, 0, 0)
+    F = inner(u, v + zero) * dx
+    fd = compute_form_data(F)
+    assert fd.num_coefficients == 1
+
+    # Check that nested zero conditionals are simplifed to zero (rank-0)
+    # and can be added to a rank-1 tensor
+    zero = conditional(z < 0, 0, conditional(z == 0, 0, 0))
+    F = inner(u, v + zero) * dx
+    fd = compute_form_data(F)
+    assert fd.num_coefficients == 1
diff --git a/ufl/algorithms/check_arities.py b/ufl/algorithms/check_arities.py
index e1d9b366b..d38f53165 100644
--- a/ufl/algorithms/check_arities.py
+++ b/ufl/algorithms/check_arities.py
@@ -57,7 +57,8 @@ def sum(self, o, a, b):
         """Apply to sum."""
         if a != b:
             raise ArityMismatch(
-                f"Adding expressions with non-matching form arguments {_afmt(a)} vs {_afmt(b)}."
+                f"Adding expressions with non-matching form arguments "
+                f"{tuple(map(_afmt, a))} vs {tuple(map(_afmt, b))}."
             )
         return a
 
@@ -86,7 +87,7 @@ def product(self, o, a, b):
             if len(c) != len(a) + len(b) or len(c) != len({x[0] for x in c}):
                 raise ArityMismatch(
                     "Multiplying expressions with overlapping form arguments "
-                    f"{_afmt(a)} vs {_afmt(b)}."
+                    f"{tuple(map(_afmt, a))} vs {tuple(map(_afmt, b))}."
                 )
             # It's fine for argument parts to overlap
             return c
@@ -138,7 +139,7 @@ def variable(self, o, f, a):
     def conditional(self, o, c, a, b):
         """Apply to conditional."""
         if c:
-            raise ArityMismatch(f"Condition cannot depend on form arguments ({_afmt(a)}).")
+            raise ArityMismatch("Condition cannot depend on form arguments.")
         if a and isinstance(o.ufl_operands[2], Zero):
             # Allow conditional(c, arg, 0)
             return a
@@ -153,7 +154,7 @@ def conditional(self, o, c, a, b):
             # conditional(c, test, nonzeroconstant)
             raise ArityMismatch(
                 "Conditional subexpressions with non-matching form arguments "
-                f"{_afmt(a)} vs {_afmt(b)}."
+                f"{tuple(map(_afmt, a))} vs {tuple(map(_afmt, b))}."
             )
 
     def linear_indexed_type(self, o, a, i):
diff --git a/ufl/conditional.py b/ufl/conditional.py
index 117808c2b..5f802943a 100644
--- a/ufl/conditional.py
+++ b/ufl/conditional.py
@@ -264,10 +264,23 @@ class Conditional(Operator):
     In C++ these take the format `(condition ? true_value : false_value)`.
     """
 
-    __slots__ = ()
+    __slots__ = ("_initialised",)
+
+    def __new__(cls, condition, true_value, false_value):
+        """Create a new Conditional."""
+        # Simplify
+        if bool(true_value == false_value):
+            return true_value
+        # Construct a new instance to be initialised
+        self = Operator.__new__(cls)
+        self._initialised = False
+        return self
 
     def __init__(self, condition, true_value, false_value):
         """Initialise."""
+        if self._initialised:
+            return
+        # Checks
         if not isinstance(condition, Condition):
             raise ValueError("Expecting condition as first argument.")
         true_value = as_ufl(true_value)
@@ -290,8 +303,8 @@ def __init__(self, condition, true_value, false_value):
                 )
             ):
                 raise ValueError("Non-scalar == or != is not allowed.")
-
         Operator.__init__(self, (condition, true_value, false_value))
+        self._initialised = True
 
     def evaluate(self, x, mapping, component, index_values):
         """Evaluate."""