diff --git a/hugr-core/src/extension/simple_op.rs b/hugr-core/src/extension/simple_op.rs
index 41e94ee58..c77ed5edc 100644
--- a/hugr-core/src/extension/simple_op.rs
+++ b/hugr-core/src/extension/simple_op.rs
@@ -26,6 +26,8 @@ pub enum OpLoadError {
     NotMember(String),
     #[error("Type args invalid: {0}.")]
     InvalidArgs(#[from] SignatureError),
+    #[error("OpDef belongs to extension {0}, expected {1}.")]
+    WrongExtension(ExtensionId, ExtensionId),
 }
 
 impl<T> NamedOp for T
@@ -51,6 +53,9 @@ pub trait MakeOpDef: NamedOp {
     /// Return the signature (polymorphic function type) of the operation.
     fn signature(&self) -> SignatureFunc;
 
+    /// The ID of the extension this operation is defined in.
+    fn extension(&self) -> ExtensionId;
+
     /// Description of the operation. By default, the same as `self.name()`.
     fn description(&self) -> String {
         self.name().to_string()
@@ -138,11 +143,20 @@ impl<T: MakeOpDef> MakeExtensionOp for T {
 
 /// Load an [MakeOpDef] from its name.
 /// See [strum_macros::EnumString].
-pub fn try_from_name<T>(name: &OpNameRef) -> Result<T, OpLoadError>
+pub fn try_from_name<T>(name: &OpNameRef, def_extension: &ExtensionId) -> Result<T, OpLoadError>
 where
     T: std::str::FromStr + MakeOpDef,
 {
-    T::from_str(name).map_err(|_| OpLoadError::NotMember(name.to_string()))
+    let op = T::from_str(name).map_err(|_| OpLoadError::NotMember(name.to_string()))?;
+    let expected_extension = op.extension();
+    if def_extension != &expected_extension {
+        return Err(OpLoadError::WrongExtension(
+            def_extension.clone(),
+            expected_extension,
+        ));
+    }
+
+    Ok(op)
 }
 
 /// Wrap an [MakeExtensionOp] with an extension registry to allow type computation.
@@ -245,6 +259,10 @@ mod test {
         fn from_def(_op_def: &OpDef) -> Result<Self, OpLoadError> {
             Ok(Self::Dumb)
         }
+
+        fn extension(&self) -> ExtensionId {
+            EXT_ID.to_owned()
+        }
     }
     const_extension_ids! {
         const EXT_ID: ExtensionId = "DummyExt";
diff --git a/hugr-core/src/std_extensions/arithmetic/conversions.rs b/hugr-core/src/std_extensions/arithmetic/conversions.rs
index b6dcab87b..5125d3a60 100644
--- a/hugr-core/src/std_extensions/arithmetic/conversions.rs
+++ b/hugr-core/src/std_extensions/arithmetic/conversions.rs
@@ -36,7 +36,11 @@ pub enum ConvertOpDef {
 
 impl MakeOpDef for ConvertOpDef {
     fn from_def(op_def: &OpDef) -> Result<Self, OpLoadError> {
-        crate::extension::simple_op::try_from_name(op_def.name())
+        crate::extension::simple_op::try_from_name(op_def.name(), op_def.extension())
+    }
+
+    fn extension(&self) -> ExtensionId {
+        EXTENSION_ID.to_owned()
     }
 
     fn signature(&self) -> SignatureFunc {
diff --git a/hugr-core/src/std_extensions/arithmetic/float_ops.rs b/hugr-core/src/std_extensions/arithmetic/float_ops.rs
index 72601c2a3..b098d89dd 100644
--- a/hugr-core/src/std_extensions/arithmetic/float_ops.rs
+++ b/hugr-core/src/std_extensions/arithmetic/float_ops.rs
@@ -44,7 +44,11 @@ pub enum FloatOps {
 
 impl MakeOpDef for FloatOps {
     fn from_def(op_def: &OpDef) -> Result<Self, OpLoadError> {
-        crate::extension::simple_op::try_from_name(op_def.name())
+        crate::extension::simple_op::try_from_name(op_def.name(), op_def.extension())
+    }
+
+    fn extension(&self) -> ExtensionId {
+        EXTENSION_ID.to_owned()
     }
 
     fn signature(&self) -> SignatureFunc {
diff --git a/hugr-core/src/std_extensions/arithmetic/int_ops.rs b/hugr-core/src/std_extensions/arithmetic/int_ops.rs
index 546b2b6c3..a302100b2 100644
--- a/hugr-core/src/std_extensions/arithmetic/int_ops.rs
+++ b/hugr-core/src/std_extensions/arithmetic/int_ops.rs
@@ -100,7 +100,11 @@ pub enum IntOpDef {
 
 impl MakeOpDef for IntOpDef {
     fn from_def(op_def: &OpDef) -> Result<Self, crate::extension::simple_op::OpLoadError> {
-        crate::extension::simple_op::try_from_name(op_def.name())
+        crate::extension::simple_op::try_from_name(op_def.name(), op_def.extension())
+    }
+
+    fn extension(&self) -> ExtensionId {
+        EXTENSION_ID.to_owned()
     }
 
     fn signature(&self) -> SignatureFunc {
diff --git a/hugr-core/src/std_extensions/logic.rs b/hugr-core/src/std_extensions/logic.rs
index d6e51811f..52e3904ad 100644
--- a/hugr-core/src/std_extensions/logic.rs
+++ b/hugr-core/src/std_extensions/logic.rs
@@ -72,7 +72,11 @@ impl MakeOpDef for NaryLogic {
     }
 
     fn from_def(op_def: &OpDef) -> Result<Self, OpLoadError> {
-        try_from_name(op_def.name())
+        try_from_name(op_def.name(), op_def.extension())
+    }
+
+    fn extension(&self) -> ExtensionId {
+        EXTENSION_ID.to_owned()
     }
 
     fn post_opdef(&self, def: &mut OpDef) {
@@ -127,6 +131,10 @@ impl MakeOpDef for NotOp {
         }
     }
 
+    fn extension(&self) -> ExtensionId {
+        EXTENSION_ID.to_owned()
+    }
+
     fn signature(&self) -> SignatureFunc {
         FunctionType::new_endo(type_row![BOOL_T]).into()
     }