diff --git a/.buildbot.sh b/.buildbot.sh
index 7bdb7b0514306..7a1976d063bb1 100755
--- a/.buildbot.sh
+++ b/.buildbot.sh
@@ -6,16 +6,16 @@ YKSOMV=4d3679fca1139876adccdbd9a27f110b91b229fa
 GRMTOOLSV=7fff436c3659f103eac658e68808990410d2594b
 set -e
 
-# This is needed because Alloy is rebased on top of rustc, and we need enough
-# depth for the bootstrapper to find the correct llvm sha
-git fetch --unshallow
-
 export CARGO_HOME="$(pwd)/.cargo"
 export RUSTUP_HOME="$(pwd)/.rustup"
 
 # Ensure the build fails if it uses excessive amounts of memory.
 ulimit -d $((1024 * 1024 * 18)) # 18 GiB
 
+if $(git rev-parse --is-shallow-repository); then
+    git fetch --unshallow
+fi
+
 /usr/bin/time -v python3 x.py test --stage 2 --config .buildbot.config.toml --exclude rustdoc-json --exclude debuginfo
 
 # Install rustup