diff --git a/mira/metamodel/template_model.py b/mira/metamodel/template_model.py
index 8570ced4..fc59a7ec 100644
--- a/mira/metamodel/template_model.py
+++ b/mira/metamodel/template_model.py
@@ -1,3 +1,5 @@
+import copy
+
 from pydantic import ConfigDict
 
 __all__ = [
@@ -473,6 +475,8 @@ def from_json(cls, data) -> "TemplateModel":
         :
             Returns the newly created template model.
         """
+        # Do a copy just to make sure we don't modify the original data
+        data = copy.deepcopy(data)
         local_symbols = {p: sympy.Symbol(p) for p in data.get("parameters", [])}
         for template_dict in data.get("templates", []):
             # We need to figure out the template class based on the type
diff --git a/mira/metamodel/templates.py b/mira/metamodel/templates.py
index df477822..88523a00 100644
--- a/mira/metamodel/templates.py
+++ b/mira/metamodel/templates.py
@@ -3,6 +3,8 @@
 
 Regenerate the JSON schema by running ``python -m mira.metamodel.schema``.
 """
+import copy
+
 from pydantic import ConfigDict
 from typing import Literal
 
@@ -376,6 +378,8 @@ def from_json(cls, data) -> "Concept":
         if isinstance(data, Concept):
             return data
         elif data.get('units'):
+            # Copy so we don't update the input
+            data = copy.deepcopy(data)
             data['units'] = Unit.from_json(data['units'])
 
         return cls(**data)
@@ -413,6 +417,8 @@ def from_json(cls, data, rate_symbols=None) -> "Template":
         :
             A Template object
         """
+        # Make a copy to make sure we don't update the input
+        data = copy.deepcopy(data)
         # We make sure to use data such that it's not modified in place,
         # e.g., we don't use pop or overwrite items, otherwise this function
         # would have unintended side effects.
diff --git a/mira/metamodel/units.py b/mira/metamodel/units.py
index 1b28ec2f..ad87d049 100644
--- a/mira/metamodel/units.py
+++ b/mira/metamodel/units.py
@@ -42,8 +42,8 @@ class Unit(BaseModel):
 
     @classmethod
     def from_json(cls, data: Dict[str, Any]) -> "Unit":
-        # Use get_sympy from amr.petrinet, but avoid circular import
-        from mira.sources.amr.petrinet import get_sympy
+        # Use get_sympy from sources, but avoid circular import
+        from mira.sources.util import get_sympy
         new_data = data.copy()
         new_data["expression"] = get_sympy(data, local_dict=UNIT_SYMBOLS)
         assert (new_data.get('expression') is None or