diff --git a/common.c b/common.c
index 6210011..6320afd 100644
--- a/common.c
+++ b/common.c
@@ -550,11 +550,10 @@ struct config_schema
 	const char *comment;                ///< User-readable description
 
 	enum config_item_type type;         ///< Required type
-	bool is_nullable;                   ///< Can be null?
 	const char *default_;               ///< Default as a configuration snippet
 
 	/// Check if the new value can be accepted.
-	/// If this is not defined, only "type" and "is_nullable" is considered.
+	/// If this is not defined, only "type" and having a default is considered.
 	bool (*validate) (struct config_item_ *, const struct config_item_ *);
 
 	/// The value has changed. Only appliable to objects.
@@ -696,7 +695,7 @@ config_schema_accepts_type
 	if (config_item_type_is_string (self->type)
 	 && config_item_type_is_string (type))
 		return true;
-	return self->is_nullable && type == CONFIG_ITEM_NULL;
+	return !self->default_ && type == CONFIG_ITEM_NULL;
 
 }
 
@@ -717,7 +716,7 @@ config_item_set_from (struct config_item_ *self, struct config_item_ *source,
 	{
 		error_set (e, "invalid type of value, expected: %s%s",
 			config_item_type_name (schema->type),
-			schema->is_nullable ? " (or null)" : "");
+			!schema->default_ ? " (or null)" : "");
 		return false;
 	}