diff --git a/modules/media/media.cc b/modules/media/media.cc
index b4e0799b0..34db62ea8 100644
--- a/modules/media/media.cc
+++ b/modules/media/media.cc
@@ -88,14 +88,12 @@ write_file(const m::room &room,
 			pathbuf, pathlen + copy(pathpart, hash)
 		};
 
-		if(!fs::exists(path))
-			wrote += size(fs::write(path, block));
-
+		wrote += size(fs::overwrite(path, block));
 		off += blksz;
 	}
 
 	assert(off == size(content));
-	assert(wrote <= off);
+	assert(wrote == off);
 	return wrote;
 }
 
@@ -151,6 +149,16 @@ read_each_block(const m::room &room,
 			fs::read(path, buf)
 		};
 
+		if(unlikely(size(block) != blksz)) throw error
+		{
+			"File [%s] block [%s] (%s) blksz %zu != %zu",
+			string_view{room.room_id},
+			string_view{at<"event_id"_>(event)},
+			path,
+			blksz,
+			size(block)
+		};
+
 		assert(size(block) == blksz);
 		ret += size(block);
 		closure(block);
diff --git a/modules/media/thumbnail.cc b/modules/media/thumbnail.cc
index df885534c..c3888971c 100644
--- a/modules/media/thumbnail.cc
+++ b/modules/media/thumbnail.cc
@@ -281,32 +281,32 @@ get__thumbnail_local(client &client,
 		client, http::OK, content_type, file_size
 	};
 
-	size_t sent{0};
-	const auto sink{[&client, &sent]
+	size_t sent_size{0};
+	const auto sink{[&client, &sent_size]
 	(const const_buffer &block)
 	{
-		sent += client.write_all(block);
+		sent_size += client.write_all(block);
 	}};
 
-	const size_t read
+	const size_t read_size
 	{
 		read_each_block(room, sink)
 	};
 
-	if(unlikely(read != file_size)) log::error
+	if(unlikely(read_size != file_size)) log::error
 	{
 		media_log, "File %s/%s [%s] size mismatch: expected %zu got %zu",
 		hostname,
 		mediaid,
 		string_view{room.room_id},
 		file_size,
-		read
+		read_size
 	};
 
 	// Have to kill client here after failing content length expectation.
-	if(unlikely(read != file_size))
+	if(unlikely(read_size != file_size))
 		client.close(net::dc::RST, net::close_ignore);
 
-	assert(read == sent);
+	assert(read_size == sent_size);
 	return response;
 }