diff --git a/lib/api/github.js b/lib/api/github.js
index 9e4cda775714b7452ed6a793a8bb7212d90c9ab8..1b768922be8c4097cc7250c7cd7a038c7d3af094 100644
--- a/lib/api/github.js
+++ b/lib/api/github.js
@@ -635,7 +635,7 @@ async function getPr(prNo) {
         pr.canRebase = true;
       }
     }
-    if (pr.base.sha !== config.baseCommitSHA) {
+    if (!pr.base || pr.base.sha !== config.baseCommitSHA) {
       pr.isStale = true;
     }
   }