Index: trunk/ppMerge/src/ppMergeCombine.c
===================================================================
--- trunk/ppMerge/src/ppMergeCombine.c	(revision 16950)
+++ trunk/ppMerge/src/ppMergeCombine.c	(revision 16989)
@@ -133,4 +133,10 @@
         while ((cell = pmFPAviewNextCell(view, fpa, 1))) {
             cellNum++;
+
+            pmHDU *hdu = pmHDUGetLowest(data->out, chip, cell); // HDU for cell
+            if (!hdu || hdu->blankPHU) {
+                pmCellWrite(cell, data->outFile, config->database, true); // Write header only
+                continue;
+            }
             if (cell->hdu) {
                 // Data will exist soon
@@ -138,5 +144,4 @@
                 chip->data_exists = cell->data_exists = true;
             }
-            pmCellWrite(cell, data->outFile, config->database, true); // Write header only
             pmReadout *readout = pmReadoutAlloc(cell); // Output readout of interest
             psArray *stack = psArrayAlloc(filenames->n); // Stack of readouts to combine
@@ -155,5 +160,4 @@
 
             // Put version metadata into header
-            pmHDU *hdu = pmHDUFromCell(cell);
             if (hdu && hdu != lastHDU) {
                 if (!hdu->header) {