diff --git a/package/tree/tree.mk b/package/tree/tree.mk
index 7c111b47d2..da0acbae49 100644
--- a/package/tree/tree.mk
+++ b/package/tree/tree.mk
@@ -11,7 +11,8 @@ TREE_LICENSE = GPL-2.0+
 TREE_LICENSE_FILES = LICENSE
 
 define TREE_BUILD_CMDS
-	$(MAKE) $(TARGET_CONFIGURE_OPTS) -C $(@D)
+	$(MAKE) $(TARGET_CONFIGURE_OPTS) CFLAGS="$(TARGET_CFLAGS) -std=c99" \
+		-C $(@D)
 endef
 
 define TREE_INSTALL_TARGET_CMDS