diff --git a/include/c64_sid.mfk b/include/c64_sid.mfk
index 1db9861f..9709ceca 100644
--- a/include/c64_sid.mfk
+++ b/include/c64_sid.mfk
@@ -24,5 +24,9 @@ byte sid_v3_cr    @$D412
 byte sid_v3_ad    @$D413
 byte sid_v3_sr    @$D414
 
+word sid_filt_cutoff @$D415
+byte sid_filt_cr @$D417
+byte sid_filt_mode @$D418
+
 volatile byte sid_paddle_x @$D419
 volatile byte sid_paddle_y @$D41A