diff --git a/nasal_gc.h b/nasal_gc.h
index cae2b12..0c9f9dd 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -106,13 +106,13 @@ struct nasal_hash// 56 bytes
 
 struct nasal_func// 112 bytes
 {
-    uint32_t dynpara;                         // dynamic parameter index in hash. index 0 is reserved for 'me'.
+    int32_t dynpara;                          // dynamic parameter name index in hash.
     uint32_t entry;                           // pc will set to entry-1 to call this function
     std::vector<nasal_ref> local;             // local scope with default value(nasal_ref)
     std::vector<nasal_ref> upvalue;           // closure
     std::unordered_map<std::string,int> keys; // parameter name table
 
-    nasal_func():dynpara(0){}
+    nasal_func():dynpara(-1){}
     void clear();
 };
 
@@ -265,7 +265,7 @@ void nasal_hash::print()
 /*functions of nasal_func*/
 void nasal_func::clear()
 {
-    dynpara=0;
+    dynpara=-1;
     local.clear();
     upvalue.clear();
     keys.clear();
diff --git a/nasal_vm.h b/nasal_vm.h
index 351b1fc..d96c1d4 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -665,7 +665,7 @@ inline void nasal_vm::opr_callfv()
     for(uint32_t i=0;i<min_size;++i)
         closure[i+1]=args[i];
     // load dynamic argument if args_size>=para_size
-    if(func.dynpara)
+    if(func.dynpara>=0)
     {
         nasal_ref vec=gc.alloc(vm_vec);
         for(uint32_t i=para_size;i<args_size;++i)
@@ -690,7 +690,7 @@ inline void nasal_vm::opr_callfh()
     gc.local.back().vec()->elems=func.local;
     // load parameters
     auto& closure=gc.local.back().vec()->elems;
-    if(func.dynpara)
+    if(func.dynpara>=0)
         die("callfh: special call cannot use dynamic argument");
 
     for(auto& i:func.keys)