diff --git a/nomsu_compiler.lua b/nomsu_compiler.lua
index 0fc3166..e2b0d89 100644
--- a/nomsu_compiler.lua
+++ b/nomsu_compiler.lua
@@ -617,7 +617,7 @@ do
   end
   NomsuCompiler.run_lua = function(self, lua)
     local lua_string = tostring(lua)
-    local run_lua_fn, err = load(lua_string, nil and tostring(source or lua.source), "t", self.environment)
+    local run_lua_fn, err = load(lua_string, tostring(source or lua.source), "t", self.environment)
     if not run_lua_fn then
       local line_numbered_lua = concat((function()
         local _accum_0 = { }
@@ -702,9 +702,18 @@ do
             args = _accum_0
           end
           local ret = compile_action(self, tree, unpack(args))
-          if not ret then
+          if ret == nil then
             local info = debug.getinfo(compile_action, "S")
-            self:compile_error(tree, "The compile-time action here (" .. tostring(stub) .. ") failed to produce any Lua", "Look at the implementation of (" .. tostring(stub) .. ") in " .. tostring(info.short_src:sub(1, 200)) .. ":" .. tostring(info.linedefined) .. " and make sure it's returning Lua code.")
+            local filename = Source:from_string(info.source).filename
+            self:compile_error(tree, "The compile-time action here (" .. tostring(stub) .. ") failed to return any value.", "Look at the implementation of (" .. tostring(stub) .. ") in " .. tostring(filename) .. ":" .. tostring(info.linedefined) .. " and make sure it's returning something.")
+          end
+          if AST.is_syntax_tree(ret) then
+            if ret == tree then
+              local info = debug.getinfo(compile_action, "S")
+              local filename = Source:from_string(info.source).filename
+              self:compile_error(tree, "The compile-time action here (" .. tostring(stub) .. ") is producing an endless loop.", "Look at the implementation of (" .. tostring(stub) .. ") in " .. tostring(filename) .. ":" .. tostring(info.linedefined) .. " and make sure it's not just returning the original tree.")
+            end
+            return self:compile(ret, compile_actions)
           end
           return ret
         end
diff --git a/nomsu_compiler.moon b/nomsu_compiler.moon
index 05c7449..2f79a34 100644
--- a/nomsu_compiler.moon
+++ b/nomsu_compiler.moon
@@ -355,7 +355,7 @@ with NomsuCompiler
 
     .run_lua = (lua)=>
         lua_string = tostring(lua)
-        run_lua_fn, err = load(lua_string, nil and tostring(source or lua.source), "t", @environment)
+        run_lua_fn, err = load(lua_string, tostring(source or lua.source), "t", @environment)
         if not run_lua_fn
             line_numbered_lua = concat(
                 [format("%3d|%s",i,line) for i, line in ipairs Files.get_lines(lua_string)],
@@ -403,11 +403,20 @@ with NomsuCompiler
                     -- Force Lua to avoid tail call optimization for debugging purposes
                     -- TODO: use tail call?
                     ret = compile_action(@, tree, unpack(args))
-                    if not ret
+                    if ret == nil
                         info = debug.getinfo(compile_action, "S")
+                        filename = Source\from_string(info.source).filename
                         @compile_error tree,
-                            "The compile-time action here (#{stub}) failed to produce any Lua",
-                            "Look at the implementation of (#{stub}) in #{info.short_src\sub(1,200)}:#{info.linedefined} and make sure it's returning Lua code."
+                            "The compile-time action here (#{stub}) failed to return any value.",
+                            "Look at the implementation of (#{stub}) in #{filename}:#{info.linedefined} and make sure it's returning something."
+                    if AST.is_syntax_tree(ret)
+                        if ret == tree
+                            info = debug.getinfo(compile_action, "S")
+                            filename = Source\from_string(info.source).filename
+                            @compile_error tree,
+                                "The compile-time action here (#{stub}) is producing an endless loop.",
+                                "Look at the implementation of (#{stub}) in #{filename}:#{info.linedefined} and make sure it's not just returning the original tree."
+                        return @compile(ret, compile_actions)
                     return ret
 
                 lua = LuaCode.Value(tree.source)