diff --git a/.cirrus.yml b/.cirrus.yml
index ac682e50a2..bed135c3f9 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -1,4 +1,6 @@
 env:
+  ### cirrus config
+  CIRRUS_CLONE_DEPTH: 1
   ### compiler options
   HOST:
   WRAPPER_CMD:
@@ -53,11 +55,11 @@ cat_logs_snippet: &CAT_LOGS
 
 merge_base_script_snippet: &MERGE_BASE
   merge_base_script:
-    - if [ "$CIRRUS_PR" = "" ]; then exit 0; fi
-    - git fetch $CIRRUS_REPO_CLONE_URL $CIRRUS_BASE_BRANCH
     - git config --global user.email "ci@ci.ci"
     - git config --global user.name "ci"
-    - git merge FETCH_HEAD  # Merge base to detect silent merge conflicts
+    - if [ "$CIRRUS_PR" = "" ]; then exit 0; fi
+    - git fetch --depth=1 $CIRRUS_REPO_CLONE_URL "pull/${CIRRUS_PR}/merge"
+    - git checkout FETCH_HEAD  # Use merged changes to detect silent merge conflicts
 
 linux_container_snippet: &LINUX_CONTAINER
   container: