diff --git a/compress.c b/compress.c
index 85a96df..e5831e8 100644
--- a/compress.c
+++ b/compress.c
@@ -28,7 +28,7 @@ int ZEXPORT compress2 (dest, destLen, source, sourceLen, level)
 {
     z_stream stream;
     int err;
-    const uInt max = -1;
+    const uInt max = (uInt)0 - 1;
     uLong left;
 
     left = *destLen;
diff --git a/uncompr.c b/uncompr.c
index 2ec3eba..f3f883a 100644
--- a/uncompr.c
+++ b/uncompr.c
@@ -30,7 +30,7 @@ int ZEXPORT uncompress (dest, destLen, source, sourceLen)
 {
     z_stream stream;
     int err;
-    const uInt max = -1;
+    const uInt max = (uInt)0 - 1;
     uLong left;
     Byte buf[1];    /* for detection of incomplete stream when *destLen == 0 */