Index: trunk/Ohana/src/libfits/matrix/F_compress_M.c
===================================================================
--- trunk/Ohana/src/libfits/matrix/F_compress_M.c	(revision 18375)
+++ trunk/Ohana/src/libfits/matrix/F_compress_M.c	(revision 18403)
@@ -19,7 +19,8 @@
 
 # define MOD_KEYWORD(ZNAME,NAME,TYPE,IN,OUT) { \
-  gfits_scan (header, ZNAME, TYPE, 1, IN); \
-  gfits_delete (header, ZNAME, 1); \
-  gfits_modify (header, NAME, TYPE, 1, OUT); }
+    if (gfits_scan (header, ZNAME, TYPE, 1, IN)) { \
+      gfits_modify (header, NAME, TYPE, 1, OUT); \
+    } \
+    gfits_delete (header, ZNAME, 1); }
 
 # define MOD_KEYWORD_REQUIRED(ZNAME,NAME,TYPE,IN,OUT) { \
@@ -147,8 +148,25 @@
     gfits_delete (header, "ZTENSION", 1);
     gfits_modify_extended (header, exttype, "Image extension");
-    // XXX validate that exttype == 'IMAGE'?
-
-    MOD_KEYWORD ("ZPCOUNT",  "PCOUNT",   "%d", &header->pcount, header->pcount);
-    MOD_KEYWORD ("ZGCOUNT",  "GCOUNT",   "%d", &header->gcount, header->gcount);
+
+    // we may have an uncompressed PCOUNT / GCOUNT value, otherwise set to 0,1
+    if (gfits_scan (header, "ZPCOUNT", "%d", 1, &header->pcount)) {
+	gfits_delete (header, "ZPCOUNT", 1);
+	gfits_modify (header, "PCOUNT", "%d", 1, header->pcount);
+    } else {
+	header->pcount = 0;
+	gfits_modify (header, "PCOUNT", "%d", 1, header->pcount);
+    }
+    if (gfits_scan (header, "ZGCOUNT", "%d", 1, &header->gcount)) {
+	gfits_delete (header, "ZGCOUNT", 1);
+	gfits_modify (header, "GCOUNT", "%d", 1, header->gcount);
+    } else {
+	header->pcount = 1;
+	gfits_modify (header, "GCOUNT", "%d", 1, header->gcount);
+    }
+  } else {
+    header->pcount = 0;
+    header->gcount = 1;
+    gfits_modify (header, "PCOUNT", "%d", 1, header->pcount);
+    gfits_modify (header, "GCOUNT", "%d", 1, header->gcount);
   }