diff -ur cdrtools-1.10/mkisofs/mkisofs.c cdrtools-1.10-zisofs/mkisofs/mkisofs.c
--- cdrtools-1.10/mkisofs/mkisofs.c	Fri Apr 20 08:45:50 2001
+++ cdrtools-1.10-zisofs/mkisofs/mkisofs.c	Thu May  3 21:59:56 2001
@@ -565,10 +565,8 @@
 	'\0', "#", "Set numbers of load sectors", ONE_DASH},
 	{{"boot-info-table", no_argument, NULL, OPTION_BOOT_INFO_TABLE},
 	'\0', NULL, "Patch boot image with info table", ONE_DASH},
-#ifdef ERIC_neverdef
 	{{"transparent-compression", no_argument, NULL, 'z'},
 	'z', NULL, "Enable transparent compression of files", ONE_DASH},
-#endif
 #ifdef APPLE_HYB
 	{{"hfs-type", required_argument, NULL, OPTION_HFS_TYPE},
 	'\0', "TYPE", "Set HFS default TYPE", ONE_DASH},
diff -ur cdrtools-1.10/mkisofs/rock.c cdrtools-1.10-zisofs/mkisofs/rock.c
--- cdrtools-1.10/mkisofs/rock.c	Tue Jan 23 04:28:34 2001
+++ cdrtools-1.10-zisofs/mkisofs/rock.c	Fri May  4 02:34:25 2001
@@ -45,7 +45,7 @@
 #define PX_SIZE 36
 #define RE_SIZE 4
 #define SL_SIZE 20
-#define ZZ_SIZE 15
+#define ZF_SIZE 16
 #ifdef APPLE_HYB
 #define AA_SIZE 14	/* size of Apple extension */
 #endif	/* APPLE_HYB */
@@ -577,17 +577,24 @@
 #ifndef VMS
 	/*
 	 * If transparent compression was requested, fill in the correct field
-	 * for this file
+	 * for this file, if (and only if) it is actually a compressed file!
+	 * This relies only on magic number, but it should in general not
+	 * be an issue since if you're using -z odds are most of your
+	 * files are already compressed.
+	 *
+	 * In the future it would be nice if mkisofs actually did the
+	 * compression.
 	 */
-	if (transparent_compression &&
-		S_ISREG(lstatbuf->st_mode) &&
-		strlen(name) > 3 &&
-		strcmp(name + strlen(name) - 3, ".gZ") == 0) {
-		FILE           *zipfile;
+	if (transparent_compression && S_ISREG(lstatbuf->st_mode)) {
+	  	static const unsigned char zisofs_magic[8] =
+			{ 0x37, 0xE4, 0x53, 0x96, 0xC9, 0xDB, 0xD6, 0x07 };
+		FILE	       *zffile;
 		char           *checkname;
 		unsigned int    file_size;
-		unsigned char   header[8];
+		unsigned char   header[16];
 		int             OK_flag;
+		int		blocksize;
+		int		headersize;
 
 		/*
 		 * First open file and verify that the correct algorithm was
@@ -596,73 +603,43 @@
 		file_size = 0;
 		OK_flag = 1;
 
-		zipfile = fopen(whole_name, "rb");
-		fread(header, 1, sizeof(header), zipfile);
+		memset(header, 0, sizeof(header));
 
-		/* Check some magic numbers from gzip. */
-		if (header[0] != 0x1f || header[1] != 0x8b || header[2] != 8)
-			OK_flag = 0;
-		/* Make sure file was blocksized. */
-		if (((header[3] & 0x40) == 0))
-			OK_flag = 0;
-		/* OK, now go to the end of the file and get some more info */
-		if (OK_flag) {
-			int	status;
-
-			status = (long) lseek(fileno(zipfile), (off_t)(-8),
-								SEEK_END);
-			if (status == -1)
+		zffile = fopen(whole_name, "rb");
+		if ( zffile ) {
+			if ( fread(header, 1, sizeof(header), zffile) != sizeof(header) )
 				OK_flag = 0;
-		}
-		if (OK_flag) {
-			if (read(fileno(zipfile), (char *) header,
-					sizeof(header)) != sizeof(header)) {
+			
+			/* Check magic number */
+			if ( memcmp(header, zisofs_magic, sizeof zisofs_magic) )
 				OK_flag = 0;
-			} else {
-				int             blocksize;
 
-				blocksize = (header[3] << 8) | header[2];
-				file_size = ((unsigned int) header[7] << 24) |
-					((unsigned int) header[6] << 16) |
-					((unsigned int) header[5] << 8) |
-							header[4];
-#if 0
-				fprintf(stderr, "Blocksize = %d %d\n",
-						blocksize, file_size);
-#endif
-				if (blocksize != SECTOR_SIZE)
-					OK_flag = 0;
-			}
-		}
-		fclose(zipfile);
-
-		checkname = strdup(whole_name);
-		checkname[strlen(whole_name) - 3] = 0;
-		zipfile = fopen(checkname, "rb");
-		if (zipfile) {
+			/* Get the real size of the file */
+			file_size = get_731(header+8);
+			
+			/* Get the header size (>> 2) */
+			headersize = header[12];
+			
+			/* Get the block size (log2) */
+			blocksize = header[13];
+			
+			fclose(zffile);
+		} else {
 			OK_flag = 0;
-#ifdef	USE_LIBSCHILY
-			errmsg(
-			"Unable to insert transparent compressed file - name conflict\n");
-#else
-			fprintf(stderr,
-			"Unable to insert transparent compressed file - name conflict\n");
-#endif
-			fclose(zipfile);
 		}
-		free(checkname);
-
+		
 		if (OK_flag) {
-			if (MAYBE_ADD_CE_ENTRY(ZZ_SIZE))
+			if (MAYBE_ADD_CE_ENTRY(ZF_SIZE))
 				add_CE_entry();
 			Rock[ipnt++] = 'Z';
-			Rock[ipnt++] = 'Z';
-			Rock[ipnt++] = ZZ_SIZE;
+			Rock[ipnt++] = 'F';
+			Rock[ipnt++] = ZF_SIZE;
 			Rock[ipnt++] = SU_VERSION;
-			Rock[ipnt++] = 'g';	/* Identify compression
-						   technique used */
+			Rock[ipnt++] = 'p'; /* Algorithm: "paged zlib" */
 			Rock[ipnt++] = 'z';
-			Rock[ipnt++] = 3;
+			/* 2 bytes for algorithm-specific information */
+			Rock[ipnt++] = headersize;
+			Rock[ipnt++] = blocksize;
 			set_733((char *) Rock + ipnt, file_size); /* Real file size */
 			ipnt += 8;
 		};