diff --git a/src/pretix/base/invoice.py b/src/pretix/base/invoice.py
index c20b3c1205..f9f93fde65 100644
--- a/src/pretix/base/invoice.py
+++ b/src/pretix/base/invoice.py
@@ -192,8 +192,15 @@ class ThumbnailingImageReader(ImageReader):
             size=(int(width * dpi / 72), int(height * dpi / 72)),
             resample=BICUBIC
         )
+        self._data = None
         return width, height
 
+    def _jpeg_fh(self):
+        # Bypass a reportlab-internal optimization that falls back to the original
+        # file handle if the file is a JPEG, and therefore does not respect the
+        # (smaller) size of the modified image.
+        return None
+
 
 class ClassicInvoiceRenderer(BaseReportlabInvoiceRenderer):
     identifier = 'classic'