diff --git a/libtransmission/cache.cc b/libtransmission/cache.cc
index f25985eb4..e8a680147 100644
--- a/libtransmission/cache.cc
+++ b/libtransmission/cache.cc
@@ -89,8 +89,14 @@ int Cache::writeContiguous(CIter const begin, CIter const end) const
     TR_ASSERT(std::size(buf) == buflen);
 
     // save it
-    auto* const tor = torrents_.get(begin->key.first);
-    auto const loc = tor->blockLoc(begin->key.second);
+    auto const& [torrent_id, block] = begin->key;
+    auto* const tor = torrents_.get(torrent_id);
+    if (tor == nullptr)
+    {
+        return EINVAL;
+    }
+
+    auto const loc = tor->blockLoc(block);
 
     if (auto const err = tr_ioWrite(tor, loc, std::size(buf), std::data(buf)); err != 0)
     {