diff --git a/src/errors.h b/src/errors.h
index 6ef4700..1c1b146 100644
--- a/src/errors.h
+++ b/src/errors.h
@@ -1802,7 +1802,8 @@
 	INIT(= N_("E704: Funcref variable name must start with a capital: %s"));
 EXTERN char e_variable_name_conflicts_with_existing_function_str[]
 	INIT(= N_("E705: Variable name conflicts with existing function: %s"));
-// E706 unused
+EXTERN char e_argument_of_str_must_be_list_string_or_dictionary[]
+	INIT(= N_("E706: Argument of %s must be a List, String or Dictionary"));
 EXTERN char e_function_name_conflicts_with_variable_str[]
 	INIT(= N_("E707: Function name conflicts with variable: %s"));
 EXTERN char e_slice_must_come_last[]