diff --git a/include/xo/reader/define_xs.hpp b/include/xo/reader/define_xs.hpp
index 41bf90d4..162bd62a 100644
--- a/include/xo/reader/define_xs.hpp
+++ b/include/xo/reader/define_xs.hpp
@@ -21,6 +21,7 @@ namespace xo {
             static std::unique_ptr<define_xs> def_0(rp<DefineExprAccess> def_expr);
 
             virtual bool admits_definition() const override;
+            virtual bool admits_symbol() const override;
             // virtual void on_f64(..) override
             virtual void on_expr(ref::brw<Expression> expr,
                                  exprstatestack * p_stack,
diff --git a/src/reader/define_xs.cpp b/src/reader/define_xs.cpp
index 5da374ad..6fa1bc45 100644
--- a/src/reader/define_xs.cpp
+++ b/src/reader/define_xs.cpp
@@ -47,6 +47,38 @@ namespace xo {
             return false;
         }
 
+        bool
+        define_xs::admits_symbol() const {
+            switch (exs_type_) {
+            case exprstatetype::expect_toplevel_expression_sequence:
+                /* unreachable */
+                assert(false);
+                return false;
+
+            case exprstatetype::def_0:
+            case exprstatetype::def_1:
+            case exprstatetype::def_2:
+            case exprstatetype::def_3:
+            case exprstatetype::def_4:
+            case exprstatetype::def_5:
+                return false;
+
+            case exprstatetype::lparen_0:
+            case exprstatetype::lparen_1:
+            case exprstatetype::expect_rhs_expression:
+            case exprstatetype::expect_symbol:
+            case exprstatetype::expect_type:
+            case exprstatetype::expr_progress:
+            case exprstatetype::invalid:
+            case exprstatetype::n_exprstatetype:
+                /* unreachable */
+                assert(false);
+                return false;
+            }
+
+            return false;
+        }
+
         void
         define_xs::on_expr(ref::brw<Expression> expr,
                            exprstatestack * /* p_stack */,
diff --git a/src/reader/parser.cpp b/src/reader/parser.cpp
index e5700bdd..f503932c 100644
--- a/src/reader/parser.cpp
+++ b/src/reader/parser.cpp
@@ -94,12 +94,16 @@ namespace xo {
         exprstate::admits_symbol() const {
             switch (exs_type_) {
             case exprstatetype::expect_toplevel_expression_sequence:
+                return false;
+
             case exprstatetype::def_0:
             case exprstatetype::def_1:
             case exprstatetype::def_2:
             case exprstatetype::def_3:
             case exprstatetype::def_4:
             case exprstatetype::def_5:
+                /* unreachable */
+                assert(false);
                 return false;
 
             case exprstatetype::lparen_0: