diff --git a/nomsu.lua b/nomsu.lua
index ff1e3fe..a600e9b 100644
--- a/nomsu.lua
+++ b/nomsu.lua
@@ -173,6 +173,9 @@ run = function()
       nomsu_environment._1_parsed(NomsuCode:from(source, code))
       print("Parse succeeded: " .. tostring(filename))
     elseif args.compile then
+      if filename:match("%.lua$") then
+        error("Cannot compile a lua file (expected a nomsu file as input)")
+      end
       local output
       if filename == 'stdin' then
         output = io.output()
diff --git a/nomsu.moon b/nomsu.moon
index fc2fe5a..a55ace4 100755
--- a/nomsu.moon
+++ b/nomsu.moon
@@ -142,6 +142,8 @@ run = ->
             print("Parse succeeded: #{filename}")
         elseif args.compile
             -- Compile .nom files into .lua
+            if filename\match("%.lua$")
+                error("Cannot compile a lua file (expected a nomsu file as input)")
             output = if filename == 'stdin' then io.output()
             else io.open(filename\gsub("%.nom$", ".lua"), "w")
             code = Files.read(filename)