Index: trunk/ppMerge/src/ppMergeCombine.c
===================================================================
--- trunk/ppMerge/src/ppMergeCombine.c	(revision 10367)
+++ trunk/ppMerge/src/ppMergeCombine.c	(revision 10527)
@@ -136,4 +136,7 @@
             pmHDU *hdu = pmHDUFromCell(cell);
             if (hdu && hdu != lastHDU) {
+                if (!hdu->header) {
+                    hdu->header = psMetadataAlloc();
+                }
                 ppMergeVersionMetadata(hdu->header);
                 lastHDU = hdu;