Index: /trunk/ppMerge/src/ppMergeCombine.c
===================================================================
--- /trunk/ppMerge/src/ppMergeCombine.c	(revision 13623)
+++ /trunk/ppMerge/src/ppMergeCombine.c	(revision 13624)
@@ -163,6 +163,7 @@
                     // Only reading and writing the first readout in each cell (plane 0)
                     if (pmReadoutReadNext(stack->data[i], fits, 0, options->rows)) {
-                        // If the mask value is set, we want to generate a mask
-                        if (options->combine->maskVal) {
+                        // If we're creating a bias or a dark, we don't want to generate a mask
+                        if ((options->zero || options->scale || options->shutter || options->mask) &&
+                            options->combine->maskVal) {
                             pmReadoutSetMask(stack->data[i], options->satMask, options->badMask);
                         }