diff --git a/element_animal/genotyping.py b/element_animal/genotyping.py
index 8bb07bf..cd42346 100644
--- a/element_animal/genotyping.py
+++ b/element_animal/genotyping.py
@@ -14,7 +14,7 @@ def activate(
     subject_schema_name: str = None,
     create_schema: bool = True,
     create_tables: bool = True,
-    linking_module: str = None,
+    linking_module = None,
 ):
     """Activate this schema.
 
diff --git a/element_animal/injection.py b/element_animal/injection.py
index ee73184..2e12bd4 100644
--- a/element_animal/injection.py
+++ b/element_animal/injection.py
@@ -16,7 +16,7 @@ def activate(
     *,
     create_schema: bool = True,
     create_tables: bool = True,
-    linking_module: str = None,
+    linking_module = None,
 ):
     """Activate this schema.
 
diff --git a/element_animal/subject.py b/element_animal/subject.py
index 7eca71b..61c3da3 100644
--- a/element_animal/subject.py
+++ b/element_animal/subject.py
@@ -11,7 +11,7 @@ def activate(
     *,
     create_schema: bool = True,
     create_tables: bool = True,
-    linking_module: str = None,
+    linking_module = None,
 ):
     """Activate this schema.
 
diff --git a/element_animal/surgery.py b/element_animal/surgery.py
index 48b0644..a08b7d5 100644
--- a/element_animal/surgery.py
+++ b/element_animal/surgery.py
@@ -16,7 +16,7 @@ def activate(
     *,
     create_schema: bool = True,
     create_tables: bool = True,
-    linking_module: str = None,
+    linking_module = None,
 ):
     """Activate this schema.