Index: src/OFMutableZIPArchiveEntry.m
==================================================================
--- src/OFMutableZIPArchiveEntry.m
+++ src/OFMutableZIPArchiveEntry.m
@@ -26,11 +26,11 @@
 
 @implementation OFMutableZIPArchiveEntry
 @dynamic fileName, fileComment, extraField, versionMadeBy, minVersionNeeded;
 @dynamic modificationDate, compressionMethod, compressedSize, uncompressedSize;
 @dynamic CRC32, versionSpecificAttributes, generalPurposeBitFlag;
-@dynamic of_localFileHeaderOffset;
+@dynamic of_startDiskNumber, of_localFileHeaderOffset;
 /*
  * The following are optional in OFMutableArchiveEntry, but Apple GCC 4.0.1 is
  * buggy and needs this to stop complaining.
  */
 @dynamic POSIXPermissions, ownerAccountID, groupOwnerAccountID;
@@ -170,10 +170,15 @@
 
 - (void)setGeneralPurposeBitFlag: (uint16_t)generalPurposeBitFlag
 {
 	_generalPurposeBitFlag = generalPurposeBitFlag;
 }
+
+- (void)of_setStartDiskNumber: (uint32_t)startDiskNumber
+{
+	_startDiskNumber = startDiskNumber;
+}
 
 - (void)of_setLocalFileHeaderOffset: (int64_t)localFileHeaderOffset
 {
 	if (localFileHeaderOffset < 0)
 		@throw [OFInvalidArgumentException exception];

Index: src/OFZIPArchive.m
==================================================================
--- src/OFZIPArchive.m
+++ src/OFZIPArchive.m
@@ -152,29 +152,38 @@
 
 @implementation OFZIPArchive
 @synthesize delegate = _delegate, archiveComment = _archiveComment;
 
 static void
-seekOrThrowInvalidFormat(OFZIPArchive *archive, const uint32_t *diskNumber,
+seekOrThrowInvalidFormat(OFZIPArchive *archive, const uint32_t *diskNumberPtr,
     OFStreamOffset offset, OFSeekWhence whence)
 {
-	if (diskNumber != NULL && *diskNumber != archive->_diskNumber) {
+	uint32_t diskNumber = 1;
+
+	if (diskNumberPtr != NULL) {
+		diskNumber = *diskNumberPtr;
+
+		if (diskNumber == 0)
+			diskNumber = 1;
+	}
+
+	if (diskNumberPtr != NULL && diskNumber != archive->_diskNumber) {
 		OFStream *oldStream = archive->_stream;
 		OFSeekableStream *stream;
 
 		if (archive->_mode != modeRead ||
-		    *diskNumber > archive->_lastDiskNumber)
+		    diskNumber > archive->_lastDiskNumber)
 			@throw [OFInvalidFormatException exception];
 
 		stream = [archive->_delegate archive: archive
-				   wantsPartNumbered: *diskNumber
+				   wantsPartNumbered: diskNumber
 				      lastPartNumber: archive->_lastDiskNumber];
 
 		if (stream == nil)
 			@throw [OFInvalidFormatException exception];
 
-		archive->_diskNumber = *diskNumber;
+		archive->_diskNumber = diskNumber;
 		archive->_stream = [stream retain];
 		[oldStream release];
 	}
 
 	@try {
@@ -229,10 +238,14 @@
 			if (![stream isKindOfClass: [OFSeekableStream class]])
 				@throw [OFInvalidArgumentException exception];
 
 			[self of_readZIPInfo];
 			[self of_readEntries];
+		} else if (_mode == modeWrite) {
+			_diskNumber = 1;
+			_lastDiskNumber = 1;
+			_centralDirectoryDisk = 1;
 		}
 
 		if (_mode == modeAppend) {
 			_offset = _centralDirectoryOffset;
 			seekOrThrowInvalidFormat(self, NULL,
@@ -341,14 +354,14 @@
 		 * FIXME: Handle number of the disk containing ZIP64 end of
 		 * central directory record.
 		 */
 		diskNumber = [_stream readLittleEndianInt32];
 		offset64 = [_stream readLittleEndianInt64];
-		_lastDiskNumber = [_stream readLittleEndianInt32];
+		_diskNumber = _lastDiskNumber = [_stream readLittleEndianInt32];
+
 		if (_lastDiskNumber == 0)
 			@throw [OFInvalidFormatException exception];
-		_lastDiskNumber--;
 
 		if (offset64 < 0 || (OFStreamOffset)offset64 != offset64)
 			@throw [OFOutOfRangeException exception];
 
 		seekOrThrowInvalidFormat(self, &diskNumber,
@@ -364,11 +377,14 @@
 		/* version made by */
 		[_stream readLittleEndianInt16];
 		/* version needed to extract */
 		[_stream readLittleEndianInt16];
 
-		if ([_stream readLittleEndianInt32] != _diskNumber)
+		diskNumber = [_stream readLittleEndianInt32];
+		if (diskNumber == 0)
+			diskNumber = 1;
+		if (diskNumber != _diskNumber)
 			@throw [OFInvalidFormatException exception];
 
 		_centralDirectoryDisk = [_stream readLittleEndianInt32];
 		_centralDirectoryEntriesInDisk =
 		    [_stream readLittleEndianInt64];
@@ -577,10 +593,11 @@
 	entry.minVersionNeeded = (entry.minVersionNeeded & 0xFF00) | 45;
 	entry.compressedSize = 0;
 	entry.uncompressedSize = 0;
 	entry.CRC32 = 0;
 	entry.generalPurposeBitFlag |= (seekable ? 0 : (1u << 3)) | (1u << 11);
+	entry.of_startDiskNumber = _diskNumber;
 	entry.of_localFileHeaderOffset = _offset;
 
 	[_stream writeLittleEndianInt32: 0x04034B50];
 	[_stream writeLittleEndianInt16: entry.minVersionNeeded];
 	[_stream writeLittleEndianInt16: entry.generalPurposeBitFlag];

Index: src/OFZIPArchiveEntry+Private.h
==================================================================
--- src/OFZIPArchiveEntry+Private.h
+++ src/OFZIPArchiveEntry+Private.h
@@ -28,10 +28,12 @@
     OF_METHOD_FAMILY(init) OF_DIRECT;
 - (uint64_t)of_writeToStream: (OFStream *)stream OF_DIRECT;
 @end
 
 @interface OFMutableZIPArchiveEntry ()
+@property (readwrite, nonatomic, setter=of_setStartDiskNumber:)
+    uint32_t of_startDiskNumber;
 @property (readwrite, nonatomic, setter=of_setLocalFileHeaderOffset:)
     int64_t of_localFileHeaderOffset;
 @end
 
 OF_ASSUME_NONNULL_END