diff --git a/nnef/src/ast/dump_doc.rs b/nnef/src/ast/dump_doc.rs
index 7483e4b33c..c103c65251 100644
--- a/nnef/src/ast/dump_doc.rs
+++ b/nnef/src/ast/dump_doc.rs
@@ -37,7 +37,7 @@ impl<'a> DocDumper<'a> {
             Dumper::new(&Nnef::default(), self.w).fragment_decl(&fragment_decl)?;
         }
         // Generate and write Primitive declarations.
-        for primitive in registry.primitives.values().flatten().sorted_by_key(|v| &v.decl.id) {
+        for primitive in registry.primitives.values().sorted_by_key(|v| &v.decl.id) {
             primitive.docstrings.iter().flatten()
                 .try_for_each(|d| writeln!(self.w, "# {d}"))?;
             
diff --git a/nnef/src/deser.rs b/nnef/src/deser.rs
index 0e32d66b03..03c4cc4268 100644
--- a/nnef/src/deser.rs
+++ b/nnef/src/deser.rs
@@ -224,7 +224,9 @@ impl<'mb> ModelBuilder<'mb> {
                 );
             }
         }
-        for registry in &self.framework.registries {
+
+        // We start with the registry that has been added last
+        for registry in self.framework.registries.iter().rev() {
             if self.registries.contains(&registry.id) {
                 if let Some(outputs) = registry
                     .deserialize(self, invocation, dt)
diff --git a/nnef/src/framework.rs b/nnef/src/framework.rs
index 4ee5edd766..582374c58d 100644
--- a/nnef/src/framework.rs
+++ b/nnef/src/framework.rs
@@ -57,20 +57,6 @@ impl Nnef {
         self
     }
 
-    pub fn with_primitive_alternative(
-        mut self,
-        registry_id: &str,
-        op_id: &str,
-        func: ToTract,
-    ) -> TractResult<Self> {
-        if let Some(reg) = self.registries.iter_mut().find(|it| it.id == registry_id.into()) {
-            reg.register_primitive_alternative(op_id, func).with_context(|| {
-                anyhow!("Impossible to add new primitive alternative for op {}", op_id)
-            })?;
-        }
-        Ok(self)
-    }
-
     pub fn enable_tract_resource(&mut self) {
         self.registries.push(crate::ops::tract_core());
     }
diff --git a/nnef/src/registry.rs b/nnef/src/registry.rs
index 654d365883..a6162684b1 100644
--- a/nnef/src/registry.rs
+++ b/nnef/src/registry.rs
@@ -41,7 +41,7 @@ pub struct Registry {
     pub docstrings: Option<Vec<String>>,
     pub aliases: Vec<Identifier>,
     pub fragments: HashMap<Identifier, FragmentDef>,
-    pub primitives: HashMap<Identifier, Vec<PrimitiveDecl>>,
+    pub primitives: HashMap<Identifier, PrimitiveDecl>,
     pub unit_element_wise_ops: Vec<(Identifier, Box<dyn ElementWiseMiniOp>)>,
     pub element_wise_ops: Vec<(Identifier, TypeId, FromTract, Vec<ast::Parameter>, ToTract)>,
     pub binary_ops: Vec<BinOp>,
@@ -89,36 +89,12 @@ impl Registry {
             results: results.iter().cloned().map(|it| it.into()).collect(),
         };
         let primitive_decl = PrimitiveDecl { decl, docstrings: None, to_tract: func };
-        self.primitives.insert(id.clone(), vec![primitive_decl]);
+        self.primitives.insert(id.clone(), primitive_decl);
         self.primitives
             .get_mut(&id)
-            .and_then(|it| it.last_mut())
             .expect("Unexpected empty entry in primitives hashmap")
     }
 
-    pub fn register_primitive_alternative(
-        &mut self,
-        id: impl AsRef<str>,
-        func: ToTract,
-    ) -> TractResult<&mut PrimitiveDecl> {
-        let id: Identifier = id.as_ref().into();
-        self.primitives.get_mut(&id).map_or_else(
-            || bail!("No primitive with name '{}' in registry: {}", id.as_ref(), self.id.as_ref()),
-            |it| -> TractResult<()> {
-                let last = it.last().unwrap_or_else(|| panic!("Unexpected empty primitive declaration for '{}'", id.as_ref()));
-                let mut new = last.clone();
-                new.to_tract = func;
-                it.insert(0, new);
-                Ok(())
-            },
-        )?;
-        Ok(self
-            .primitives
-            .get_mut(&id)
-            .and_then(|it| it.last_mut())
-            .expect("Unexpected empty entry in primitives hashmap"))
-    }
-
     pub fn register_fragment(&mut self, def: FragmentDef) {
         self.fragments.insert(def.decl.id.clone(), def);
     }
@@ -189,28 +165,14 @@ impl Registry {
         invocation: &ast::Invocation,
         dt: &[Option<DatumType>],
     ) -> TractResult<Option<Value>> {
-        if let Some(p) = self.primitives.get(&invocation.id) {
-            let out_value = p
-                .iter()
-                .enumerate()
-                .find_map(|(idx, op)| {
-                    let resolved = ResolvedInvocation {
-                        invocation,
-                        default_params: &op.decl.parameters,
-                        dt_from_quant_file: dt,
-                    };
-                    (op.to_tract)(builder, &resolved)
-                        .map_err(|err| {
-                            log::debug!(
-                                "Failed to load {:?} with deserializer {}: {:?}",
-                                &invocation.id,
-                                idx,
-                                &err
-                            );
-                        })
-                        .ok()
-                })
-                .ok_or(anyhow!("No valid deserializer found for {:?}", &invocation.id))?;
+        if let Some(op) = self.primitives.get(&invocation.id) {
+            let resolved = ResolvedInvocation {
+                invocation,
+                default_params: &op.decl.parameters,
+                dt_from_quant_file: dt,
+            };
+            let out_value = (op.to_tract)(builder, &resolved)
+                .with_context(|| format!("Deserializing op `{}'", invocation.id.0))?;
             return Ok(Some(out_value));
         }
         if let Some(ew) = self.unit_element_wise_ops.iter().find(|ew| ew.0 == invocation.id) {