diff --git a/lib/carto/parser.js b/lib/carto/parser.js
index d98d9a0..81b1e64 100644
--- a/lib/carto/parser.js
+++ b/lib/carto/parser.js
@@ -414,7 +414,7 @@ carto.Parser = function Parser(env) {
                 // needs to be careful to warn when unsupported operations are used.
                 field: function() {
                     if (! $('[')) return;
-                    var field_name = $(/(^[a-zA-Z0-9\-_]+)/);
+                    var field_name = $(/(^[\:a-zA-Z0-9\-_]+)/);
                     if (! $(']')) return;
                     if (field_name) return new tree.Field(field_name[1]);
                 },