diff --git a/.github/scripts/util.sh b/.github/scripts/util.sh
index af2d51019..564dde43b 100644
--- a/.github/scripts/util.sh
+++ b/.github/scripts/util.sh
@@ -103,6 +103,7 @@ build_ac_xts() {
                     CFLAGS="$CFLAGS -Wno-error=incompatible-function-pointer-types"
                 fi
             fi
+            CFLAGS="$CFLAGS -std=gnu89 -Wno-error=implicit-function-declaration -Wno-implicit-int"
             ./autogen.sh --prefix=$X11_PREFIX CFLAGS="$CFLAGS"
             if [ "$X11_OS" = "Darwin" ]; then
                 make -j${FDO_CI_CONCURRENT:-4} install tetexec.cfg