diff --git a/crates/graph/src/builder.rs b/crates/graph/src/builder.rs
index c5acb4f..ad1590a 100644
--- a/crates/graph/src/builder.rs
+++ b/crates/graph/src/builder.rs
@@ -1,9 +1,9 @@
-use crate::node::{AsyncRuleNode, ConstNode, Node, NodeValue, RuleNode};
+use crate::node::{AsyncRuleNode, ConstNode, InvalidatableConstNode, Node, NodeValue, RuleNode};
 use crate::rule::{AsyncRule, Rule};
 use crate::util;
 use crate::{
     Asynchronous, ErasedNode, Graph, Input, InvalidationSignal, NodeGraph, NodeId, Synchronicity,
-    Synchronous,
+    Synchronous, ValueInvalidationSignal,
 };
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
@@ -57,6 +57,20 @@ impl<O: 'static, S: Synchronicity> GraphBuilder<O, S> {
         return self.add_node(ConstNode::new(value));
     }
 
+    pub fn add_invalidatable_value<V: NodeValue>(
+        &mut self,
+        value: V,
+    ) -> (Input<V>, ValueInvalidationSignal<V, S>) {
+        let input = self.add_node(InvalidatableConstNode::new(value));
+        let signal = ValueInvalidationSignal {
+            node_idx: input.node_idx,
+            value: Rc::clone(&input.value),
+            graph: Rc::clone(&self.node_graph),
+            graph_is_valid: Rc::clone(&self.is_valid),
+        };
+        (input, signal)
+    }
+
     pub fn add_rule<R>(&mut self, rule: R) -> Input<R::Output>
     where
         R: Rule,
diff --git a/crates/graph/src/lib.rs b/crates/graph/src/lib.rs
index 56249ed..6900b67 100644
--- a/crates/graph/src/lib.rs
+++ b/crates/graph/src/lib.rs
@@ -5,7 +5,7 @@ mod synchronicity;
 mod util;
 
 use builder::{BuildGraphError, GraphBuilder};
-use node::ErasedNode;
+use node::{ErasedNode, NodeValue};
 use petgraph::visit::{IntoEdgeReferences, NodeIndexable};
 use petgraph::{stable_graph::StableDiGraph, visit::EdgeRef};
 use rule::{AsyncRule, InputVisitor, Rule};
@@ -239,32 +239,48 @@ impl<S: Synchronicity> InvalidationSignal<S> {
     }
 }
 
+pub struct ValueInvalidationSignal<V, Synch: Synchronicity> {
+    node_idx: NodeId,
+    value: Rc<RefCell<Option<V>>>,
+    graph: Rc<RefCell<NodeGraph<Synch>>>,
+    graph_is_valid: Rc<Cell<bool>>,
+}
+
+impl<V: NodeValue, S: Synchronicity> ValueInvalidationSignal<V, S> {
+    pub fn set_value(&self, value: V) {
+        let mut current_value = self.value.borrow_mut();
+        if !current_value
+            .as_ref()
+            .expect("invalidatable value node must be initialized with value")
+            .node_value_eq(&value)
+        {
+            *current_value = Some(value);
+            self.graph_is_valid.set(false);
+            let mut graph = self.graph.borrow_mut();
+            let node = &mut graph[self.node_idx];
+            node.invalidate();
+        }
+    }
+}
+
 // TODO: i really want Input to be able to implement Deref somehow
 
 #[cfg(test)]
 mod tests {
     use super::*;
-
-    struct ConstantRule<T>(T);
-    impl<T: Clone + crate::node::NodeValue> Rule for ConstantRule<T> {
-        type Output = T;
-        fn visit_inputs(&self, _visitor: &mut impl InputVisitor) {}
-        fn evaluate(&mut self) -> Self::Output {
-            self.0.clone()
-        }
-    }
+    use crate::rule::ConstantRule;
 
     #[test]
     fn rule_output_with_no_inputs() {
         let mut builder = GraphBuilder::new();
-        builder.set_output(ConstantRule(1234));
+        builder.set_output(ConstantRule::new(1234));
         assert_eq!(*builder.build().unwrap().evaluate(), 1234);
     }
 
     #[test]
     fn test_output_is_valid() {
         let mut builder = GraphBuilder::new();
-        builder.set_output(ConstantRule(1));
+        builder.set_output(ConstantRule::new(1));
         let mut graph = builder.build().unwrap();
         assert!(!graph.is_output_valid());
         graph.evaluate();
@@ -298,6 +314,7 @@ mod tests {
         builder.set_output(Double(doubled));
         assert_eq!(*builder.build().unwrap().evaluate(), 168);
     }
+
     struct Inc(i32);
     impl Rule for Inc {
         type Output = i32;
@@ -406,12 +423,12 @@ mod tests {
     #[test]
     fn modify_graph() {
         let mut builder = GraphBuilder::new();
-        builder.set_output(ConstantRule(1));
+        builder.set_output(ConstantRule::new(1));
         let mut graph = builder.build().unwrap();
         assert_eq!(*graph.evaluate(), 1);
         graph = graph
             .modify(|g| {
-                g.set_output(ConstantRule(2));
+                g.set_output(ConstantRule::new(2));
             })
             .expect("modify");
         assert_eq!(*graph.evaluate(), 2);
@@ -438,7 +455,7 @@ mod tests {
     #[tokio::test]
     async fn async_graph() {
         let mut builder = GraphBuilder::new_async();
-        builder.set_output(ConstantRule(42));
+        builder.set_output(ConstantRule::new(42));
         let mut graph = builder.build().unwrap();
         assert_eq!(*graph.evaluate_async().await, 42);
     }
@@ -483,7 +500,7 @@ mod tests {
         let mut invalidate = None;
         let a = builder.add_invalidatable_rule(|inv| {
             invalidate = Some(inv);
-            ConstantRule(0)
+            ConstantRule::new(0)
         });
         struct IncAdd(Input<i32>, i32);
         impl Rule for IncAdd {
@@ -505,4 +522,17 @@ mod tests {
         assert!(!graph.is_output_valid());
         assert_eq!(*graph.evaluate(), 1);
     }
+
+    #[test]
+    fn invalidatable_value() {
+        let mut builder = GraphBuilder::new();
+        let (a, invalidate) = builder.add_invalidatable_value(0);
+        let b = builder.add_value(1);
+        builder.set_output(Add(a, b));
+        let mut graph = builder.build().unwrap();
+        assert_eq!(*graph.evaluate(), 1);
+        invalidate.set_value(42);
+        assert!(!graph.is_output_valid());
+        assert_eq!(*graph.evaluate(), 43);
+    }
 }
diff --git a/crates/graph/src/node.rs b/crates/graph/src/node.rs
index 15fafe5..8a2a7d5 100644
--- a/crates/graph/src/node.rs
+++ b/crates/graph/src/node.rs
@@ -108,6 +108,45 @@ impl<V: NodeValue, S: Synchronicity> Node<V, S> for ConstNode<V, S> {
     }
 }
 
+pub(crate) struct InvalidatableConstNode<V, S> {
+    value: Rc<RefCell<Option<V>>>,
+    valid: bool,
+    synchronicity: std::marker::PhantomData<S>,
+}
+
+impl<V, S> InvalidatableConstNode<V, S> {
+    pub(crate) fn new(value: V) -> Self {
+        Self {
+            value: Rc::new(RefCell::new(Some(value))),
+            valid: true,
+            synchronicity: std::marker::PhantomData,
+        }
+    }
+}
+
+impl<V: NodeValue, S: Synchronicity> Node<V, S> for InvalidatableConstNode<V, S> {
+    fn is_valid(&self) -> bool {
+        self.valid
+    }
+
+    fn invalidate(&mut self) {
+        self.valid = false;
+    }
+
+    fn visit_inputs(&self, _visitor: &mut dyn FnMut(NodeId) -> ()) {}
+
+    fn update(&mut self) -> S::UpdateResult<'_> {
+        self.valid = true;
+        // This node is only invalidate when node_value_eq between the old/new value is false,
+        // so it is always the case that the update method has changed the value.
+        S::make_update_result(true)
+    }
+
+    fn value_rc(&self) -> &Rc<RefCell<Option<V>>> {
+        &self.value
+    }
+}
+
 pub(crate) struct RuleNode<R, V, S> {
     rule: R,
     value: Rc<RefCell<Option<V>>>,
diff --git a/crates/graph/src/rule.rs b/crates/graph/src/rule.rs
index 61d905a..2dfe0a0 100644
--- a/crates/graph/src/rule.rs
+++ b/crates/graph/src/rule.rs
@@ -1,5 +1,7 @@
 use crate::node::NodeValue;
 use crate::Input;
+use std::cell::RefCell;
+use std::rc::Rc;
 
 pub trait Rule: 'static {
     type Output: NodeValue;
@@ -20,3 +22,21 @@ pub trait AsyncRule: 'static {
 pub trait InputVisitor {
     fn visit<T>(&mut self, input: &Input<T>);
 }
+
+pub struct ConstantRule<T>(T);
+
+impl<T> ConstantRule<T> {
+    pub fn new(value: T) -> Self {
+        Self(value)
+    }
+}
+
+impl<T: Clone + NodeValue> Rule for ConstantRule<T> {
+    type Output = T;
+
+    fn visit_inputs(&self, _visitor: &mut impl InputVisitor) {}
+
+    fn evaluate(&mut self) -> Self::Output {
+        self.0.clone()
+    }
+}