diff --git a/vhdlpp/scope.cc b/vhdlpp/scope.cc
index 3a7fdc4d7..cb20fb9f8 100644
--- a/vhdlpp/scope.cc
+++ b/vhdlpp/scope.cc
@@ -23,6 +23,7 @@
 # include  "subprogram.h"
 # include  "entity.h"
 # include  "std_funcs.h"
+# include  "std_types.h"
 # include  <algorithm>
 # include  <iostream>
 # include  <iterator>
@@ -197,7 +198,7 @@ const VTypeEnum* ScopeBase::is_enum_name(perm_string name) const
             return *it;
     }
 
-    return NULL;
+    return find_std_enum_name(name);
 }
 
 /*
diff --git a/vhdlpp/std_types.cc b/vhdlpp/std_types.cc
index 9085741ff..20acb42a6 100644
--- a/vhdlpp/std_types.cc
+++ b/vhdlpp/std_types.cc
@@ -51,6 +51,7 @@ void generate_global_types(ActiveScope*res)
       VTypeEnum*enum_BOOLEAN = new VTypeEnum(enum_BOOLEAN_vals);
       type_BOOLEAN.set_definition(enum_BOOLEAN);
       std_types[type_BOOLEAN.peek_name()] = &type_BOOLEAN;
+      std_enums.push_back(enum_BOOLEAN);
 
       res->use_name(type_BOOLEAN.peek_name(),           &type_BOOLEAN);
       res->use_name(perm_string::literal("bit"),        &primitive_BIT);
@@ -76,7 +77,7 @@ void delete_global_types()
 
 const VTypeEnum*find_std_enum_name(perm_string name)
 {
-    for(list<const VTypeEnum*>::iterator it = std_enums.begin();
+    for(list<const VTypeEnum*>::const_iterator it = std_enums.begin();
             it != std_enums.end(); ++it) {
         if((*it)->has_name(name))
             return *it;
diff --git a/vhdlpp/std_types.h b/vhdlpp/std_types.h
index 6715a4358..b38003cf4 100644
--- a/vhdlpp/std_types.h
+++ b/vhdlpp/std_types.h
@@ -27,6 +27,7 @@ int emit_packages(void);
 void generate_global_types(ActiveScope*res);
 bool is_global_type(perm_string type_name);
 void delete_global_types();
+const VTypeEnum*find_std_enum_name(perm_string name);
 
 extern const VTypePrimitive primitive_BOOLEAN;
 extern const VTypePrimitive primitive_BIT;