diff --git a/src/engine/platform/genesisext.cpp b/src/engine/platform/genesisext.cpp
index 1c44bcfb9..bfe771a6d 100644
--- a/src/engine/platform/genesisext.cpp
+++ b/src/engine/platform/genesisext.cpp
@@ -418,6 +418,16 @@ void DivPlatformGenesisExt::tick(bool sysTick) {
       }
     }
     if (writeSomething) {
+      if (chan[7].active) { // CSM
+        writeMask^=0xf0;
+      }
+      /*printf(
+        "Mask: %c %c %c %c\n",
+        (writeMask&0x10)?'1':'-',
+        (writeMask&0x20)?'2':'-',
+        (writeMask&0x40)?'3':'-',
+        (writeMask&0x80)?'4':'-'
+      );*/
       immWrite(0x28,writeMask);
     }
   }
@@ -478,6 +488,13 @@ void DivPlatformGenesisExt::tick(bool sysTick) {
     if (chan[7].active) { // CSM
       writeMask^=0xf0;
     }
+    /*printf(
+        "Mask: %c %c %c %c\n",
+        (writeMask&0x10)?'1':'-',
+        (writeMask&0x20)?'2':'-',
+        (writeMask&0x40)?'3':'-',
+        (writeMask&0x80)?'4':'-'
+      );*/
     immWrite(0x28,writeMask);
   }