diff --git a/hvcc/core/hv2ir/types/IR.py b/hvcc/core/hv2ir/types/IR.py
index dc2b9d2..06169a5 100644
--- a/hvcc/core/hv2ir/types/IR.py
+++ b/hvcc/core/hv2ir/types/IR.py
@@ -1,5 +1,5 @@
 from pydantic import BaseModel, RootModel
-from typing import List, Optional, Union, Literal
+from typing import Dict, List, Optional, Union, Literal
 
 
 IRConnectionType = Literal["-->", "~i>", "~f>", "signal"]
@@ -39,7 +39,7 @@ class IRNode(BaseModel):
 
 
 class HeavyIRType(RootModel):
-    root: dict[str, IRNode]
+    root: Dict[str, IRNode]
 
 
 if __name__ == "__main__":
diff --git a/hvcc/core/hv2ir/types/Lang.py b/hvcc/core/hv2ir/types/Lang.py
index 0f790cb..2dd9c29 100644
--- a/hvcc/core/hv2ir/types/Lang.py
+++ b/hvcc/core/hv2ir/types/Lang.py
@@ -35,7 +35,7 @@ class LangNode(BaseModel):
 
 
 class HeavyLangType(RootModel):
-    root: dict[str, LangNode]
+    root: Dict[str, LangNode]
 
 
 if __name__ == "__main__":
diff --git a/hvcc/interpreters/pd2hv/PdGraph.py b/hvcc/interpreters/pd2hv/PdGraph.py
index e5a1b47..ea0eda2 100644
--- a/hvcc/interpreters/pd2hv/PdGraph.py
+++ b/hvcc/interpreters/pd2hv/PdGraph.py
@@ -118,7 +118,14 @@ def add_parsed_connection(self, from_index: int, from_outlet: int, to_index: int
                            "Have all inlets and outlets been declared?",
                            NotificationEnum.ERROR_UNABLE_TO_CONNECT_OBJECTS)
 
-    def add_hv_arg(self, arg_index: int, name: str, value_type: str, default_value: str, required: bool) -> None:
+    def add_hv_arg(
+        self,
+        arg_index: int,
+        name: str,
+        value_type: str,
+        default_value: Optional[str],
+        required: bool
+    ) -> None:
         """ Add a Heavy argument to the graph. Indicies are from zero (not one, like Pd).
         """
         # ensure that self.hv_args is big enough, as heavy arguments are not