Index: src/OFDeflateStream.m
==================================================================
--- src/OFDeflateStream.m
+++ src/OFDeflateStream.m
@@ -351,12 +351,13 @@
 		/* FIXME: This can be done more efficiently than unreading */
 		[_stream unreadFromBuffer: _buffer + _bufferIndex
 				   length: _bufferLength - _bufferIndex];
 		_bufferIndex = _bufferLength = 0;
 
-		CTX.position += [_stream readIntoBuffer: CTX.length
-						 length: 4 - CTX.position];
+		CTX.position += [_stream
+		    readIntoBuffer: CTX.length + CTX.position
+			    length: 4 - CTX.position];
 
 		if OF_UNLIKELY (CTX.position < 4)
 			return bytesWritten;
 
 		if OF_UNLIKELY ((CTX.length[0] | (CTX.length[1] << 8)) !=