diff --git a/src/Var.cc b/src/Var.cc
index b107156b3a..b7f065044b 100644
--- a/src/Var.cc
+++ b/src/Var.cc
@@ -343,6 +343,17 @@ Val* internal_val(const char* name)
 	return id->ID_Val();
 	}
 
+Val* internal_const_val(const char* name)
+	{
+	ID* id = lookup_ID(name, GLOBAL_MODULE_NAME);
+	if ( ! id )
+		internal_error("internal variable %s missing", name);
+	if ( ! id->IsConst())
+		internal_error("internal variable %s is not constant", name);
+
+	return id->ID_Val();
+	}
+
 Val* opt_internal_val(const char* name)
 	{
 	ID* id = lookup_ID(name, GLOBAL_MODULE_NAME);
diff --git a/src/Var.h b/src/Var.h
index 3be8ecc079..f1cbcda87b 100644
--- a/src/Var.h
+++ b/src/Var.h
@@ -27,6 +27,7 @@ extern void begin_func(ID* id, const char* module_name, function_flavor flavor,
 extern void end_func(Stmt* body, attr_list* attrs = 0);
 
 extern Val* internal_val(const char* name);
+extern Val* internal_const_val(const char* name); // internal error if not const
 extern Val* opt_internal_val(const char* name);	// returns nil if not defined
 extern double opt_internal_double(const char* name);
 extern bro_int_t opt_internal_int(const char* name);
diff --git a/src/builtin-func.y b/src/builtin-func.y
index 3fe67db1dd..cfd5459bb1 100644
--- a/src/builtin-func.y
+++ b/src/builtin-func.y
@@ -466,7 +466,7 @@ const_def:	TOK_CONST opt_ws TOK_ID opt_ws ':' opt_ws TOK_ID opt_ws ';'
 					decl.c_namespace_start.c_str(), 
 					builtin_types[typeidx].c_type, decl.bare_name.c_str(), 
 					decl.c_namespace_end.c_str());
-			fprintf(fp_netvar_init, "\t%s = internal_val(\"%s\")%s;\n",
+			fprintf(fp_netvar_init, "\t%s = internal_const_val(\"%s\")%s;\n",
 				decl.c_fullname.c_str(), decl.bro_fullname.c_str(),
 				accessor);
 			}