1 files changed, 4 insertions, 0 deletions
diff --git a/tools/upbc.lua b/tools/upbc.lua
index 9d9531c..a538b1c 100644
--- a/tools/upbc.lua
+++ b/tools/upbc.lua
@@ -23,6 +23,10 @@ for _, argument in ipairs(arg) do
       return 1
     end
   else
+    if src then
+      print("upbc can only handle one input file at a time.")
+      return 1
+    end
     src = argument
   end
 end