diff --git a/toml.cm b/toml.cm
index bcea35fc..1ba4ba3c 100644
--- a/toml.cm
+++ b/toml.cm
@@ -211,8 +211,13 @@ function encode_toml(obj) {
   }
 
   function quote_key(k) {
-    if (search(k, '.') != null || search(k, '"') != null || search(k, ' ') != null) {
-      return '"' + toml_escape(k) + '"'
+    var i = 0
+    var c = null
+    for (i = 0; i < length(k); i++) {
+      c = k[i]
+      if (!((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_' || c == '-')) {
+        return '"' + toml_escape(k) + '"'
+      }
     }
     return k
   }