diff --git a/src/cs_ident.cc b/src/cs_ident.cc
index 22b8e26..a3c1967 100644
--- a/src/cs_ident.cc
+++ b/src/cs_ident.cc
@@ -114,12 +114,9 @@ alias_impl::alias_impl(state &cs, string_ref name, any_value v, int fl):
     p_initial.val_s = v;
 }
 
-void alias_impl::push_arg(ident_stack &st, bool um) {
+void alias_impl::push_arg(ident_stack &st) {
     st.next = p_astack;
     p_astack = &st;
-    if (um) {
-        p_flags &= ~IDENT_FLAG_UNKNOWN;
-    }
 }
 
 void alias_impl::pop_arg() {
@@ -142,7 +139,7 @@ void alias_impl::set_arg(thread_state &ts, any_value &v) {
     if (ident_is_used_arg(this, ts)) {
         p_astack->code = bcode_ref{};
     } else {
-        push_arg(ts.idstack.emplace_back(*ts.pstate), false);
+        push_arg(ts.idstack.emplace_back(*ts.pstate));
         ts.callstack->usedargs[get_index()] = true;
     }
     p_astack->val_s = std::move(v);
@@ -389,14 +386,16 @@ LIBCUBESCRIPT_EXPORT int command::get_num_args() const {
 /* external API for alias stack management */
 
 LIBCUBESCRIPT_EXPORT alias_stack::alias_stack(state &cs, ident *a) {
-    if (!a || !a->is_alias()) {
+    if (!a || !a->is_alias() || (a->get_flags() & IDENT_FLAG_ARG)) {
         p_alias = nullptr;
         return;
     }
-    p_alias = static_cast<alias *>(a);
-    static_cast<alias_impl *>(p_alias)->push_arg(
+    auto *aimp = static_cast<alias_impl *>(p_alias);
+    p_alias = aimp;
+    aimp->push_arg(
         cs.thread_pointer()->idstack.emplace_back(cs)
     );
+    aimp->p_flags &= ~IDENT_FLAG_UNKNOWN;
 }
 
 LIBCUBESCRIPT_EXPORT alias_stack::~alias_stack() {
diff --git a/src/cs_ident.hh b/src/cs_ident.hh
index 4b957ba..938dc73 100644
--- a/src/cs_ident.hh
+++ b/src/cs_ident.hh
@@ -96,7 +96,7 @@ struct alias_impl: ident_impl, alias {
     alias_impl(state &cs, string_ref n, int flags);
     alias_impl(state &cs, string_ref n, any_value v, int flags);
 
-    void push_arg(ident_stack &st, bool um = true);
+    void push_arg(ident_stack &st);
     void pop_arg();
     void undo_arg(ident_stack &st);
     void redo_arg(ident_stack &st);
diff --git a/src/cs_vm.cc b/src/cs_vm.cc
index f69722e..d6c9092 100644
--- a/src/cs_vm.cc
+++ b/src/cs_vm.cc
@@ -11,7 +11,9 @@ namespace cubescript {
 
 static inline void push_alias(ident *id, ident_stack &st) {
     if (id->is_alias() && !(id->get_flags() & IDENT_FLAG_ARG)) {
-        static_cast<alias_impl *>(id)->push_arg(st);
+        auto *aimp = static_cast<alias_impl *>(id);
+        aimp->push_arg(st);
+        aimp->p_flags &= ~IDENT_FLAG_UNKNOWN;
     }
 }
 
@@ -211,7 +213,7 @@ void exec_alias(
     std::size_t noff = ts.idstack.size();
     for(std::size_t i = 0; i < callargs; i++) {
         auto &ap = *static_cast<alias_impl *>(ts.istate->identmap[i]);
-        ap.push_arg(ts.idstack.emplace_back(*ts.pstate), false);
+        ap.push_arg(ts.idstack.emplace_back(*ts.pstate));
         ap.p_astack->val_s = std::move(args[offset + i]);
         uargs[i] = true;
     }
@@ -738,7 +740,7 @@ std::uint32_t *vm_exec(
                     !ident_is_used_arg(a, ts)
                 ) {
                     static_cast<alias_impl *>(a)->push_arg(
-                        ts.idstack.emplace_back(*ts.pstate), false
+                        ts.idstack.emplace_back(*ts.pstate)
                     );
                     ts.callstack->usedargs[a->get_index()] = true;
                 }
@@ -756,7 +758,7 @@ std::uint32_t *vm_exec(
                     !ident_is_used_arg(id, ts)
                 ) {
                     static_cast<alias_impl *>(id)->push_arg(
-                        ts.idstack.emplace_back(*ts.pstate), false
+                        ts.idstack.emplace_back(*ts.pstate)
                     );
                     ts.callstack->usedargs[id->get_index()] = true;
                 }