diff --git a/src/komap.py b/src/komap.py
index c82b34b..7c573c6 100644
--- a/src/komap.py
+++ b/src/komap.py
@@ -234,7 +234,10 @@ if options.renderer == "mapnik":
     if escape:
       escape = escape_sql_column
     else:
-      escape = lambda i, asname=False:'"'+i+'"'
+      def escape(i, asname=False)
+        if name in mapped_cols:
+          return name # already escaped
+        return '"'+i+'"'
     for i in itags:
       if i in numerics:
         tt.add("""(CASE WHEN %s ~ E'^[[:digit:]]+([.][[:digit:]]+)?$' THEN CAST (%s AS FLOAT) ELSE NULL END) as %s__num"""%(escape(i),escape(i),i))