diff --git a/src/calibre/utils/lzx/compressor.c b/src/calibre/utils/lzx/compressor.c
index 6f43bbc3c9..fb507e6882 100644
--- a/src/calibre/utils/lzx/compressor.c
+++ b/src/calibre/utils/lzx/compressor.c
@@ -309,18 +309,10 @@ Compressor_compress(Compressor *self, PyObject *args, PyObject *kwds)
 {
     static char *kwlist[] = {"data", "flush", NULL};
     char *data = NULL;
-    unsigned int inlen = 0;
+    Py_ssize_t inlen = 0;
     int flush = 0;
 
-    if (!PyArg_ParseTupleAndKeywords(
-#if PYTHON_MAJOR_VERSION >= 3
-            args, kwds, "y#|b", kwlist, &data, &inlen, &flush)) {
-#else
-            args, kwds, "s#|b", kwlist, &data, &inlen, &flush)) {
-#endif
-        return NULL;
-    }
-
+    if (!PyArg_ParseTupleAndKeywords(args, kwds, "y#|p", kwlist, &data, &inlen, &flush)) return NULL;
     return Compressor_compress__(self, data, inlen, flush);
 }