diff --git a/string2.lua b/string2.lua
index fe33bb9..dd0af98 100644
--- a/string2.lua
+++ b/string2.lua
@@ -26,6 +26,30 @@ isplit = function(self, sep)
     sep = sep
   }, 0
 end
+local lua_keywords = {
+  "and",
+  "break",
+  "do",
+  "else",
+  "elseif",
+  "end",
+  "false",
+  "for",
+  "function",
+  "goto",
+  "if",
+  "in",
+  "local",
+  "nil",
+  "not",
+  "or",
+  "repeat",
+  "return",
+  "then",
+  "true",
+  "until",
+  "while"
+}
 local string2 = {
   isplit = isplit,
   uppercase = upper,
@@ -107,15 +131,25 @@ local string2 = {
       end
     end)
     str = gsub(str, "^_*%d", "_%1")
-    if str.from_lua_id then
-      local re_orig = str:from_lua_id()
-      if re_orig ~= orig then
-        require('ldt').breakpoint()
+    if match(str, "^_*[a-z]*$") then
+      for _index_0 = 1, #lua_keywords do
+        local kw = lua_keywords[_index_0]
+        if match(str, ("^_*" .. kw)) then
+          str = "_" .. str
+        end
       end
     end
     return str
   end,
   from_lua_id = function(str)
+    if match(str, "^_+[a-z]*$") then
+      for _index_0 = 1, #lua_keywords do
+        local kw = lua_keywords[_index_0]
+        if match(str, ("^_+" .. kw)) then
+          str = str:sub(2, -1)
+        end
+      end
+    end
     str = gsub(str, "^_(_*%d.*)", "%1")
     str = gsub(str, "_", " ")
     str = gsub(str, "x([0-9A-F][0-9A-F])", function(hex)
diff --git a/string2.moon b/string2.moon
index 4e62e92..426504c 100644
--- a/string2.moon
+++ b/string2.moon
@@ -12,6 +12,11 @@ isplit = (sep='%s+')=>
         return i, line, start, (nl and (nl-1) or #@str)
     return step, {str:@, pos:1, :sep}, 0
 
+lua_keywords = {
+    "and", "break", "do", "else", "elseif", "end", "false", "for", "function", "goto", "if",
+    "in", "local", "nil", "not", "or", "repeat", "return", "then", "true", "until", "while"
+}
+
 string2 = {
     :isplit, uppercase:upper, lowercase:lower, reversed:reverse
     capitalized: => gsub(@, '%l', upper, 1)
@@ -59,14 +64,19 @@ string2 = {
             else format("x%02X", byte(c))
         -- Lua IDs can't start with numbers, so map "1" -> "_1", "_1" -> "__1", etc.
         str = gsub str, "^_*%d", "_%1"
-        if str.from_lua_id
-            re_orig = str\from_lua_id!
-            require('ldt').breakpoint! if re_orig != orig
+        if match str, "^_*[a-z]*$"
+            for kw in *lua_keywords
+                if match str, ("^_*"..kw)
+                    str = "_"..str
         return str
 
     -- from_lua_id(as_lua_id(str)) == str, but behavior is unspecified for inputs that
     -- did not come from as_lua_id()
     from_lua_id: (str)->
+        if match str, "^_+[a-z]*$"
+            for kw in *lua_keywords
+                if match str, ("^_+"..kw)
+                    str = str\sub(2,-1)
         str = gsub(str, "^_(_*%d.*)", "%1")
         str = gsub(str, "_", " ")
         str = gsub(str, "x([0-9A-F][0-9A-F])", (hex)-> char(tonumber(hex, 16)))