1 files changed, 4 insertions, 0 deletions
diff --git a/tools/upbc.lua b/tools/upbc.lua
index bf9a68d..bfd93f8 100644
--- a/tools/upbc.lua
+++ b/tools/upbc.lua
@@ -18,6 +18,10 @@ for _, argument in ipairs(arg) do
   if argument == "--generate-upbdefs" then
     generate_upbdefs = true
   else
+    if src then
+      print("upbc can only handle one input file at a time.")
+      return 1
+    end
     src = argument
   end
 end