diff --git a/win32port/zlib/inflate.c b/win32port/zlib/inflate.c
index 5bec31e2..664c4b9c 100644
--- a/win32port/zlib/inflate.c
+++ b/win32port/zlib/inflate.c
@@ -1472,9 +1472,10 @@ z_streamp strm;
 {
     struct inflate_state FAR *state;
 
-    if (strm == Z_NULL || strm->state == Z_NULL) return -1L << 16;
-    state = (struct inflate_state FAR *)strm->state;
-    return ((long)(state->back) << 16) +
-        (state->mode == COPY ? state->length :
-            (state->mode == MATCH ? state->was - state->length : 0));
+    if (strm == Z_NULL || strm->state == Z_NULL)
+        return (long)(((unsigned long)0 - 1) << 16);
+     state = (struct inflate_state FAR *)strm->state;
+    return (long)(((unsigned long)((long)state->back)) << 16) +
+         (state->mode == COPY ? state->length :
+             (state->mode == MATCH ? state->was - state->length : 0));
 }