diff --git a/hugr-core/src/extension.rs b/hugr-core/src/extension.rs
index 058d48aa4..c5da85276 100644
--- a/hugr-core/src/extension.rs
+++ b/hugr-core/src/extension.rs
@@ -58,10 +58,13 @@ impl ExtensionRegistry {
     ) -> Result<Self, ExtensionRegistryError> {
         let mut exts = BTreeMap::new();
         for ext in value.into_iter() {
+            let ext_v = ext.version().clone();
             let prev = exts.insert(ext.name.clone(), ext);
             if let Some(prev) = prev {
                 return Err(ExtensionRegistryError::AlreadyRegistered(
                     prev.name().clone(),
+                    prev.version().clone(),
+                    ext_v,
                 ));
             };
         }
@@ -83,13 +86,35 @@ impl ExtensionRegistry {
     /// Returns a reference to the registered extension if successful.
     pub fn register(&mut self, extension: Extension) -> Result<&Extension, ExtensionRegistryError> {
         match self.0.entry(extension.name().clone()) {
-            btree_map::Entry::Occupied(_) => Err(ExtensionRegistryError::AlreadyRegistered(
+            btree_map::Entry::Occupied(prev) => Err(ExtensionRegistryError::AlreadyRegistered(
                 extension.name().clone(),
+                prev.get().version().clone(),
+                extension.version().clone(),
             )),
             btree_map::Entry::Vacant(ve) => Ok(ve.insert(extension)),
         }
     }
 
+    /// Registers a new extension to the registry, keeping most up to date if extension exists.
+    ///
+    /// If extension IDs match, the extension with the higher version is kept.
+    /// If versions match, the original extension is kept.
+    /// Returns a reference to the registered extension if successful.
+    pub fn register_updated(
+        &mut self,
+        extension: Extension,
+    ) -> Result<&Extension, ExtensionRegistryError> {
+        match self.0.entry(extension.name().clone()) {
+            btree_map::Entry::Occupied(mut prev) => {
+                if prev.get().version() < extension.version() {
+                    *prev.get_mut() = extension;
+                }
+                Ok(prev.into_mut())
+            }
+            btree_map::Entry::Vacant(ve) => Ok(ve.insert(extension)),
+        }
+    }
+
     /// Returns the number of extensions in the registry.
     pub fn len(&self) -> usize {
         self.0.len()
@@ -328,6 +353,11 @@ impl Extension {
         &self.name
     }
 
+    /// Returns the version of the extension.
+    pub fn version(&self) -> &Version {
+        &self.version
+    }
+
     /// Iterator over the operations of this [`Extension`].
     pub fn operations(&self) -> impl Iterator<Item = (&OpName, &Arc<OpDef>)> {
         self.operations.iter()
@@ -389,8 +419,8 @@ impl PartialEq for Extension {
 #[derive(Debug, Clone, Error, PartialEq, Eq)]
 pub enum ExtensionRegistryError {
     /// Extension already defined.
-    #[error("The registry already contains an extension with id {0}.")]
-    AlreadyRegistered(ExtensionId),
+    #[error("The registry already contains an extension with id {0} and version {1}. New extension has version {2}.")]
+    AlreadyRegistered(ExtensionId, Version, Version),
     /// A registered extension has invalid signatures.
     #[error("The extension {0} contains an invalid signature, {1}.")]
     InvalidSignature(ExtensionId, #[source] SignatureError),
@@ -551,6 +581,42 @@ pub mod test {
     // We re-export this here because mod op_def is private.
     pub use super::op_def::test::SimpleOpDef;
 
+    use super::*;
+    #[test]
+    fn test_register_update() {
+        let mut reg = ExtensionRegistry::try_new([]).unwrap();
+        let ext_1_id = ExtensionId::new("ext1").unwrap();
+        let ext_2_id = ExtensionId::new("ext2").unwrap();
+        let ext1 = Extension::new(ext_1_id.clone(), Version::new(1, 0, 0));
+        let ext1_1 = Extension::new(ext_1_id.clone(), Version::new(1, 1, 0));
+        let ext1_2 = Extension::new(ext_1_id.clone(), Version::new(0, 2, 0));
+        let ext2 = Extension::new(ext_2_id, Version::new(1, 0, 0));
+
+        reg.register(ext1.clone()).unwrap();
+        assert_eq!(reg.get("ext1").unwrap().version(), &Version::new(1, 0, 0));
+
+        // normal registration fails
+        assert_eq!(
+            reg.register(ext1_1.clone()),
+            Err(ExtensionRegistryError::AlreadyRegistered(
+                ext_1_id,
+                Version::new(1, 0, 0),
+                Version::new(1, 1, 0)
+            ))
+        );
+
+        // register with update works
+        reg.register_updated(ext1_1.clone()).unwrap();
+        assert_eq!(reg.get("ext1").unwrap().version(), &Version::new(1, 1, 0));
+
+        // register with lower version does not change version
+        reg.register_updated(ext1_2.clone()).unwrap();
+        assert_eq!(reg.get("ext1").unwrap().version(), &Version::new(1, 1, 0));
+
+        reg.register(ext2.clone()).unwrap();
+        assert_eq!(reg.get("ext2").unwrap().version(), &Version::new(1, 0, 0));
+        assert_eq!(reg.len(), 2);
+    }
     mod proptest {
 
         use ::proptest::{collection::hash_set, prelude::*};