diff --git a/src/libratbag-private.h b/src/libratbag-private.h
index bc2517d4..71fd72a4 100644
--- a/src/libratbag-private.h
+++ b/src/libratbag-private.h
@@ -525,6 +525,7 @@ ratbag_resolution_set_dpi_list(struct ratbag_resolution *res,
 		if (i > 0)
 			assert(dpis[i] > dpis[i - 1]);
 	}
+	res->ndpis = ndpis;
 }
 
 static inline void