diff --git a/src/m4a.c b/src/m4a.c
index 0c68c6bddd..9877ad7401 100644
--- a/src/m4a.c
+++ b/src/m4a.c
@@ -1199,7 +1199,7 @@ void CgbSound(void)
             else
             {
                 unsigned int envMask = 0xF;
-                *nrx2ptr = (envelopeStepTimeAndDir & newMask) + (channels->envelopeVolume << 4);
+                *nrx2ptr = (envelopeStepTimeAndDir & envMask) + (channels->envelopeVolume << 4);
                 *nrx4ptr = channels->n4 | 0x80;
                 if (ch == 1 && !(*nrx0ptr & 0x08))
                     *nrx4ptr = channels->n4 | 0x80;