diff --git a/changelog.d/15876.bugfix b/changelog.d/15876.bugfix
new file mode 100644
index 0000000000000000000000000000000000000000..9dbae04c4f4033ef7070b4c52986895b25294c62
--- /dev/null
+++ b/changelog.d/15876.bugfix
@@ -0,0 +1 @@
+Correctly resize thumbnails with pillow version >=10.
diff --git a/synapse/media/thumbnailer.py b/synapse/media/thumbnailer.py
index f909a4fb9a19472e9bb2b11b1754dfc63a380f70..73d2272f0583f98cdb9304b7251da42a8ce57789 100644
--- a/synapse/media/thumbnailer.py
+++ b/synapse/media/thumbnailer.py
@@ -131,7 +131,7 @@ class Thumbnailer:
             else:
                 with self.image:
                     self.image = self.image.convert("RGB")
-        return self.image.resize((width, height), Image.ANTIALIAS)
+        return self.image.resize((width, height), Image.LANCZOS)
 
     def scale(self, width: int, height: int, output_type: str) -> BytesIO:
         """Rescales the image to the given dimensions.