diff --git a/simgear/io/HTTPClient.cxx b/simgear/io/HTTPClient.cxx
index c3d2e0ce..8a48bff6 100644
--- a/simgear/io/HTTPClient.cxx
+++ b/simgear/io/HTTPClient.cxx
@@ -47,7 +47,7 @@ const int ZLIB_INFLATE_WINDOW_BITS = -MAX_WBITS;
 const int GZIP_HEADER_ID1 = 31;
 const int GZIP_HEADER_ID2 = 139;
 const int GZIP_HEADER_METHOD_DEFLATE = 8;
-const int GZIP_HEADER_SIZE = 10;
+const unsigned int GZIP_HEADER_SIZE = 10;
 const int GZIP_HEADER_FEXTRA = 1 << 2;
 const int GZIP_HEADER_FNAME = 1 << 3;
 const int GZIP_HEADER_COMMENT = 1 << 4;