Index: trunk/psModules/src/imcombine/pmReadoutCombine.c
===================================================================
--- trunk/psModules/src/imcombine/pmReadoutCombine.c	(revision 17104)
+++ trunk/psModules/src/imcombine/pmReadoutCombine.c	(revision 17137)
@@ -87,4 +87,7 @@
         psString comment = NULL;        // Comment to add to header
         psStringAppend(&comment, "Combining using statistic: %x", params->combine);
+        if (!hdu->header) {
+            hdu->header = psMetadataAlloc();
+        }
         psMetadataAddStr(hdu->header, PS_LIST_TAIL, "HISTORY", PS_META_DUPLICATE_OK, comment, "");
         psFree(comment);