diff --git a/configure.in b/configure.in
index 3e72b41..8e867c8 100644
--- a/configure.in
+++ b/configure.in
@@ -100,6 +100,7 @@ case $host in
     PKG_CHECK_MODULES([PROXY], [libproxy-1.0],
                       [LIBS+=" ${PROXY_LIBS}"
                        CXXFLAGS+=" ${PROXY_CFLAGS}"
+                       CPPFLAGS+=" ${PROXY_CFLAGS}"
                        have_proxy=1])
     ;;
   (*mingw*|*win*)
@@ -110,6 +111,7 @@ case $host in
     PKG_CHECK_MODULES([PROXY], [libproxy-1.0],
                       [LIBS+=" ${PROXY_LIBS}"
                        CXXFLAGS+=" ${PROXY_CFLAGS}"
+                       CPPFLAGS+=" ${PROXY_CFLAGS}"
                        have_proxy=1])
     ;;
 esac