diff --git a/.gitignore b/.gitignore
index 300bb05..fb871be 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,5 @@ docs/build
 .DS_Store
 dist/
 build/
+__pycache__/
+venv/
diff --git a/flask_sieve/rules_processor.py b/flask_sieve/rules_processor.py
index a3be94b..0352619 100644
--- a/flask_sieve/rules_processor.py
+++ b/flask_sieve/rules_processor.py
@@ -194,9 +194,9 @@ def validate_dimensions(self, value, params, **kwargs):
         if not self.validate_file(value):
             return False
         try:
-            image = Image.open(value.filename)
+            image = Image.open(value)
             w, h = image.size
-            image.close()
+            value.seek(0)
             return ('%dx%d' % (w, h)) == params[0]
         except Exception:
             return False
diff --git a/tests/test_rules_processor.py b/tests/test_rules_processor.py
index 274ad60..bba2c97 100644
--- a/tests/test_rules_processor.py
+++ b/tests/test_rules_processor.py
@@ -11,10 +11,10 @@ class TestRulesProcessor(unittest.TestCase):
     def setUp(self):
         self.parser = Parser()
         self.processor = RulesProcessor()
-        self.stream = open('tests/files/image.png')
+        self.stream = open('tests/files/image.png', 'rb')
         self.image_file = FileStorage(
             stream=self.stream,
-            filename='tests/files/image.png',
+            filename='image.png',
             content_type='image/png',
             name='image'
         )