diff --git a/proto/anki/stats.proto b/proto/anki/stats.proto
index 43263ec0f..1bd0fe630 100644
--- a/proto/anki/stats.proto
+++ b/proto/anki/stats.proto
@@ -37,7 +37,8 @@ message CardStatsResponse {
     uint32 ease = 5;
     float taken_secs = 6;
     optional cards.FsrsMemoryState memory_state = 7;
-    int64 last_interval = 8;
+    // seconds
+    uint32 last_interval = 8;
   }
   repeated StatsRevlogEntry revlog = 1;
   int64 card_id = 2;