diff --git a/src/engine/platform/c64.cpp b/src/engine/platform/c64.cpp
index fd3a0e03a..fc341a9e5 100644
--- a/src/engine/platform/c64.cpp
+++ b/src/engine/platform/c64.cpp
@@ -182,6 +182,7 @@ void DivPlatformC64::tick(bool sysTick) {
           chan[i].duty-=chan[i].std.duty.val;
         }
       }
+      chan[i].duty&=4095;
       rWrite(i*7+2,chan[i].duty&0xff);
       rWrite(i*7+3,chan[i].duty>>8);
     }