diff --git a/dictionaryutils/__init__.py b/dictionaryutils/__init__.py
index aa29303..ec1b265 100644
--- a/dictionaryutils/__init__.py
+++ b/dictionaryutils/__init__.py
@@ -278,7 +278,7 @@ def allow_nulls(self):
                     if not isinstance(prop["enum"], list):
                         prop["enum"] = [prop["enum"]]
                     prop["enum"].append(None)
-                elif "anyOf" in prop:
+                elif "anyOf" in prop and {"type": "null"} not in prop["anyOf"]:
                     prop["anyOf"].append({"type": "null"})
-                elif "oneOf" in prop:
+                elif "oneOf" in prop and {"type": "null"} not in prop["oneOf"]:
                     prop["oneOf"].append({"type": "null"})
diff --git a/pyproject.toml b/pyproject.toml
index 5027554..64121aa 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "dictionaryutils"
-version = "3.4.5"
+version = "3.4.6"
 description = "Python wrapper and metaschema for datadictionary."
 authors = ["CTDS UChicago <cdis@uchicago.edu>"]
 license = "Apache-2.0"