diff --git a/ufl/action.py b/ufl/action.py
index 14267d722..f744a8be6 100644
--- a/ufl/action.py
+++ b/ufl/action.py
@@ -69,12 +69,21 @@ def __new__(cls, *args, **kw):
         if isinstance(right, (Coargument, Argument)):
             return left
 
-        if isinstance(left, (FormSum, Sum)):
-            # Action distributes over sums on the LHS
-            return FormSum(*[(Action(component, right), 1) for component in left.ufl_operands])
-        if isinstance(right, (FormSum, Sum)):
-            # Action also distributes over sums on the RHS
-            return FormSum(*[(Action(left, component), 1) for component in right.ufl_operands])
+        # Action distributes over sums on the LHS
+        if isinstance(left, Sum):
+            return FormSum(*((Action(component, right), 1) for component in left.ufl_operands))
+        elif isinstance(left, FormSum):
+            return FormSum(
+                *((Action(c, right), w) for c, w in zip(left.components(), left.weights()))
+            )
+
+        # Action also distributes over sums on the RHS
+        if isinstance(right, Sum):
+            return FormSum(*((Action(left, component), 1) for component in right.ufl_operands))
+        elif isinstance(right, FormSum):
+            return FormSum(
+                *((Action(left, c), w) for c, w in zip(right.components(), right.weights()))
+            )
 
         return super(Action, cls).__new__(cls)
 
diff --git a/ufl/adjoint.py b/ufl/adjoint.py
index 71227f578..7f1b1a556 100644
--- a/ufl/adjoint.py
+++ b/ufl/adjoint.py
@@ -49,7 +49,7 @@ def __new__(cls, *args, **kw):
             return form._form
         elif isinstance(form, FormSum):
             # Adjoint distributes over sums
-            return FormSum(*[(Adjoint(component), 1) for component in form.components()])
+            return FormSum(*((Adjoint(c), w) for c, w in zip(form.components(), form.weights())))
         elif isinstance(form, Coargument):
             # The adjoint of a coargument `c: V* -> V*` is the identity
             # matrix mapping from V to V (i.e. V x V* -> R).
diff --git a/ufl/algorithms/map_integrands.py b/ufl/algorithms/map_integrands.py
index 0a6da1817..71f7d8ff2 100644
--- a/ufl/algorithms/map_integrands.py
+++ b/ufl/algorithms/map_integrands.py
@@ -59,7 +59,7 @@ def map_integrands(function, form, only_integral_type=None):
             # Simplification of `BaseForm` objects may turn `FormSum` into a sum of `Expr` objects
             # that are not `BaseForm`, i.e. into a `Sum` object.
             # Example: `Action(Adjoint(c*), u)` with `c*` a `Coargument` and u a `Coefficient`.
-            return sum([component for component, _ in nonzero_components])
+            return sum(component * w for component, w in nonzero_components)
         return FormSum(*nonzero_components)
     elif isinstance(form, Adjoint):
         # Zeros are caught inside `Adjoint.__new__`
diff --git a/ufl/form.py b/ufl/form.py
index 274a873fd..58e2d9432 100644
--- a/ufl/form.py
+++ b/ufl/form.py
@@ -787,7 +787,7 @@ def _analyze_domains(self):
 
         # Collect unique domains
         self._domains = sort_domains(
-            join_domains(chain.from_iterable(e.ufl_domains() for e in self.ufl_operands))
+            join_domains(chain.from_iterable(c.ufl_domains() for c in self.components()))
         )
 
     def ufl_domains(self):
@@ -799,7 +799,9 @@ def ufl_domains(self):
     def __hash__(self):
         """Hash."""
         if self._hash is None:
-            self._hash = hash(tuple(hash(component) for component in self.components()))
+            self._hash = hash(
+                tuple((hash(c), hash(w)) for c, w in zip(self.components(), self.weights()))
+            )
         return self._hash
 
     def equals(self, other):
@@ -808,8 +810,10 @@ def equals(self, other):
             return False
         if self is other:
             return True
-        return len(self.components()) == len(other.components()) and all(
-            a == b for a, b in zip(self.components(), other.components())
+        return (
+            len(self.components()) == len(other.components())
+            and all(a == b for a, b in zip(self.components(), other.components()))
+            and all(a == b for a, b in zip(self.weights(), other.weights()))
         )
 
     def __str__(self):
@@ -818,7 +822,7 @@ def __str__(self):
         # warning("Calling str on form is potentially expensive and
         # should be avoided except during debugging.")
         # Not caching this because it can be huge
-        s = "\n  +  ".join(str(component) for component in self.components())
+        s = "\n  +  ".join(f"{w}*{c}" for c, w in zip(self.components(), self.weights()))
         return s or "<empty FormSum>"
 
     def __repr__(self):
@@ -827,7 +831,7 @@ def __repr__(self):
         # warning("Calling repr on form is potentially expensive and
         # should be avoided except during debugging.")
         # Not caching this because it can be huge
-        itgs = ", ".join(repr(component) for component in self.components())
+        itgs = ", ".join(f"{w!r}*{c!r}" for c, w in zip(self.components(), self.weights()))
         r = "FormSum([" + itgs + "])"
         return r
 
diff --git a/ufl/formoperators.py b/ufl/formoperators.py
index 6616c7fff..063755c46 100644
--- a/ufl/formoperators.py
+++ b/ufl/formoperators.py
@@ -319,8 +319,8 @@ def derivative(form, coefficient, argument=None, coefficient_derivatives=None):
         # Distribute derivative over FormSum components
         return FormSum(
             *[
-                (derivative(component, coefficient, argument, coefficient_derivatives), 1)
-                for component in form.components()
+                (derivative(component, coefficient, argument, coefficient_derivatives), w)
+                for component, w in zip(form.components(), form.weights())
             ]
         )
     elif isinstance(form, Adjoint):