ECM can operate at a larger CTU and transform size than VVC. To enable stronger deblocking of smooth large blocks it is proposed to increase the maximum luma deblocking length from 7 to 15 for a boundary segment that has a size orthogonal to the block boundary of 64 samples or more. The filter design is similar to the VVC deblocking design for length greater than 3. The deblocking decision for a longer filter (length 15 on at least one side) is checked if length 7 deblocking decisions are passed. The additional decision for length 15 is similar to VVC but a bit more restrictive.