diff --git a/src/pretix/control/forms/__init__.py b/src/pretix/control/forms/__init__.py
index 752b3a9182..01d673db12 100644
--- a/src/pretix/control/forms/__init__.py
+++ b/src/pretix/control/forms/__init__.py
@@ -229,7 +229,7 @@ class ExtValidationMixin:
                 raise forms.ValidationError(_("Filetype not allowed!"))
 
             if ext in IMAGE_EXTS:
-                validate_uploaded_file_for_valid_image(data)
+                validate_uploaded_file_for_valid_image(data if isinstance(data, UploadedFile) else data.file)
 
         return data
 
diff --git a/src/pretix/helpers/images.py b/src/pretix/helpers/images.py
index 728413c624..31773849f6 100644
--- a/src/pretix/helpers/images.py
+++ b/src/pretix/helpers/images.py
@@ -44,11 +44,12 @@ def validate_uploaded_file_for_valid_image(f):
     # have to read the data into memory.
     if hasattr(f, 'temporary_file_path'):
         file = f.temporary_file_path()
+    elif hasattr(f, 'read'):
+        if hasattr(f, 'seek') and callable(f.seek):
+            f.seek(0)
+        file = BytesIO(f.read())
     else:
-        if hasattr(f, 'read'):
-            file = BytesIO(f.read())
-        else:
-            file = BytesIO(f['content'])
+        file = BytesIO(f['content'])
 
     try:
         try: