diff --git a/hugr-py/src/hugr/ext.py b/hugr-py/src/hugr/ext.py
index 3910b7ae7..533e55cd7 100644
--- a/hugr-py/src/hugr/ext.py
+++ b/hugr-py/src/hugr/ext.py
@@ -218,6 +218,20 @@ def qualified_name(self) -> str:
             return f"{ext_name}.{self.name}"
         return self.name
 
+    def instantiate(
+        self,
+        args: Sequence[tys.TypeArg] | None = None,
+        concrete_signature: tys.FunctionType | None = None,
+    ) -> ops.ExtOp:
+        """Instantiate an operation from this definition.
+
+        Args:
+            args: Type arguments corresponding to the type parameters of the definition.
+            concrete_signature: Concrete function type of the operation, only required
+            if the operation is polymorphic.
+        """
+        return ops.ExtOp(self, concrete_signature, list(args or []))
+
 
 @dataclass
 class ExtensionValue(ExtensionObject):
diff --git a/hugr-py/src/hugr/ops.py b/hugr-py/src/hugr/ops.py
index 738898a75..a97470adf 100644
--- a/hugr-py/src/hugr/ops.py
+++ b/hugr-py/src/hugr/ops.py
@@ -230,7 +230,7 @@ def ext_op(self) -> ExtOp:
         Computed once using :meth:`op_def` :meth:`type_args` and :meth:`type_args`.
         Each of those methods should be deterministic.
         """
-        return ExtOp(self.op_def(), self.cached_signature(), self.type_args())
+        return self.op_def().instantiate(self.type_args(), self.cached_signature())
 
     def op_def(self) -> ext.OpDef:
         """The :class:`tys.OpDef` for this operation.
@@ -657,7 +657,7 @@ def name(self) -> str:
 class DataflowBlock(DfParentOp):
     """Parent of non-entry basic block in a control flow graph."""
 
-    #: Inputs types of the innner dataflow graph.
+    #: Inputs types of the inner dataflow graph.
     inputs: tys.TypeRow
     _sum: tys.Sum | None = None
     _other_outputs: tys.TypeRow | None = field(default=None, repr=False)
@@ -879,7 +879,7 @@ def name(self) -> str:
 class Case(DfParentOp):
     """Parent of a dataflow graph that is a branch of a :class:`Conditional`."""
 
-    #: Inputs types of the innner dataflow graph.
+    #: Inputs types of the inner dataflow graph.
     inputs: tys.TypeRow
     _outputs: tys.TypeRow | None = field(default=None, repr=False)
     num_out: int = field(default=0, repr=False)