diff --git a/hugr/src/hugr.rs b/hugr/src/hugr.rs
index 02b5a25b5..4e817d2e0 100644
--- a/hugr/src/hugr.rs
+++ b/hugr/src/hugr.rs
@@ -196,6 +196,7 @@ impl Hugr {
         extension_registry: &ExtensionRegistry,
     ) -> Result<(), ValidationError> {
         resolve_extension_ops(self, extension_registry)?;
+        self.validate_no_extensions(extension_registry)?;
         self.infer_extensions()?;
         self.validate(extension_registry)?;
         Ok(())
diff --git a/hugr/src/hugr/validate.rs b/hugr/src/hugr/validate.rs
index 26857495a..2290824cd 100644
--- a/hugr/src/hugr/validate.rs
+++ b/hugr/src/hugr/validate.rs
@@ -37,7 +37,7 @@ struct ValidationContext<'a, 'b> {
     dominators: HashMap<Node, Dominators<Node>>,
     /// Context for the extension validation.
     #[allow(dead_code)]
-    extension_validator: ExtensionValidator,
+    extension_validator: Option<ExtensionValidator>,
     /// Registry of available Extensions
     extension_registry: &'b ExtensionRegistry,
 }
@@ -51,6 +51,16 @@ impl Hugr {
         self.validate_with_extension_closure(HashMap::new(), extension_registry)
     }
 
+    /// Check the validity of the HUGR, but don't check consistency of extension
+    /// requirements between connected nodes or between parents and children.
+    pub fn validate_no_extensions(
+        &self,
+        extension_registry: &ExtensionRegistry,
+    ) -> Result<(), ValidationError> {
+        let mut validator = ValidationContext::new(self, HashMap::new(), extension_registry, false);
+        validator.validate()
+    }
+
     /// Check the validity of a hugr, taking an argument of a closure for the
     /// free extension variables
     pub fn validate_with_extension_closure(
@@ -58,7 +68,7 @@ impl Hugr {
         closure: ExtensionSolution,
         extension_registry: &ExtensionRegistry,
     ) -> Result<(), ValidationError> {
-        let mut validator = ValidationContext::new(self, closure, extension_registry);
+        let mut validator = ValidationContext::new(self, closure, extension_registry, true);
         validator.validate()
     }
 }
@@ -72,11 +82,16 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
         hugr: &'a Hugr,
         extension_closure: ExtensionSolution,
         extension_registry: &'b ExtensionRegistry,
+        validate_extensions: bool,
     ) -> Self {
         Self {
             hugr,
             dominators: HashMap::new(),
-            extension_validator: ExtensionValidator::new(hugr, extension_closure),
+            extension_validator: if validate_extensions {
+                Some(ExtensionValidator::new(hugr, extension_closure))
+            } else {
+                None
+            },
             extension_registry,
         }
     }
@@ -183,8 +198,9 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
             // If this is a container with I/O nodes, check that the extension they
             // define match the extensions of the container.
             if let Some([input, output]) = self.hugr.get_io(node) {
-                self.extension_validator
-                    .validate_io_extensions(node, input, output)?;
+                if let Some(validator) = &self.extension_validator {
+                    validator.validate_io_extensions(node, input, output)?;
+                }
             }
         }
 
@@ -248,8 +264,10 @@ impl<'a, 'b> ValidationContext<'a, 'b> {
             let other_offset = self.hugr.graph.port_offset(link).unwrap().into();
 
             #[cfg(feature = "extension_inference")]
-            self.extension_validator
-                .check_extensions_compatible(&(node, port), &(other_node, other_offset))?;
+            if let Some(validator) = &self.extension_validator {
+                validator
+                    .check_extensions_compatible(&(node, port), &(other_node, other_offset))?;
+            }
 
             let other_op = self.hugr.get_optype(other_node);
             let Some(other_kind) = other_op.port_kind(other_offset) else {