diff --git a/configure.in b/configure.in
index 7d9e31a..dc56eba 100644
--- a/configure.in
+++ b/configure.in
@@ -62,12 +62,15 @@ if test -z "$QTLIBDIR"; then
    AC_MSG_WARN(Could not locate QT 4.1)
   case $host in
     *darwin*)
+        CPPFLAGS+=" -DQ_OS_MAC"
       ;;
     *mingw*|*win*)
       LDFLAGS+=" -lwinhttp"
+        CPPFLAGS+=" -DQ_OS_WIN32"
       ;;
     *)
       LDFLAGS+=" -lproxy"
+        CPPFLAGS+=" -DQ_OS_LINUX"
       ;;
   esac
 else