diff --git a/src/reader/exprstate.cpp b/src/reader/exprstate.cpp
index 17c68eff..7e207da8 100644
--- a/src/reader/exprstate.cpp
+++ b/src/reader/exprstate.cpp
@@ -255,10 +255,13 @@ namespace xo {
             case tokentype::tk_leftangle:
             case tokentype::tk_rightangle:
             case tokentype::tk_dot:
-            case tokentype::tk_comma:
                 assert(false);
                 return;
 
+            case tokentype::tk_comma:
+                this->on_comma_token(tk, p_stack, p_emit_expr);
+                return;
+
             case tokentype::tk_colon:
                 this->on_colon_token(tk, p_stack);
                 return;