diff --git a/scripts/build.sh b/scripts/build.sh
index da80feba..83751b69 100755
--- a/scripts/build.sh
+++ b/scripts/build.sh
@@ -153,7 +153,8 @@ tools_build_muon() {
 
     pushd "${TOOLDIR}/muon" || exit 1
 
-    CC="${CC}" ninja="${SAMU}" ./bootstrap.sh stage1
+    CC="${CC}" CFLAGS="${CFLAGS} -std=c99" ninja="${SAMU}" \
+        ./bootstrap.sh stage1
 
     CC="${CC}" ninja="${SAMU}" stage1/muon setup        \
         -Dprefix="${TOOLDIR}"                           \