diff --git a/.gitignore b/.gitignore
index b6e4761..9ad24b8 100644
--- a/.gitignore
+++ b/.gitignore
@@ -50,6 +50,7 @@ coverage.xml
 *.py,cover
 .hypothesis/
 .pytest_cache/
+reports/
 
 # Translations
 *.mo
diff --git a/openapi_schema_validator/validators.py b/openapi_schema_validator/validators.py
index 555df89..8521c64 100644
--- a/openapi_schema_validator/validators.py
+++ b/openapi_schema_validator/validators.py
@@ -1,3 +1,5 @@
+from copy import deepcopy
+
 from jsonschema import _legacy_validators, _utils, _validators
 from jsonschema.validators import create
 
@@ -63,7 +65,8 @@ def __init__(self, *args, **kwargs):
 
     def iter_errors(self, instance, _schema=None):
         if _schema is None:
-            _schema = self.schema
+            # creates a copy by value from schema to prevent mutation
+            _schema = deepcopy(self.schema)
 
         # append defaults to trigger validator (i.e. nullable)
         if 'nullable' not in _schema:
diff --git a/tests/unit/test_shortcut.py b/tests/unit/test_shortcut.py
new file mode 100644
index 0000000..9832489
--- /dev/null
+++ b/tests/unit/test_shortcut.py
@@ -0,0 +1,22 @@
+from openapi_schema_validator import validate
+from unittest import TestCase
+
+
+class ValidateTest(TestCase):
+    def test_validate_does_not_mutate_schema_adding_nullable_key(self):
+        schema = {
+            "type": "object",
+            'properties': {
+                'email': {
+                    'type': 'string'
+                },
+                'enabled': {
+                    'type': 'boolean',
+                }
+            },
+            'example': {'enabled': False, 'email': "foo@bar.com"}
+        }
+
+        validate({"email": "foo@bar.com"}, schema)
+
+        self.assertTrue("nullable" not in schema["properties"]["email"].keys())