diff --git a/.buildbot.sh b/.buildbot.sh
index 12e09b518b433..5b3f52b93e219 100644
--- a/.buildbot.sh
+++ b/.buildbot.sh
@@ -14,5 +14,5 @@ export RUSTUP_HOME="`pwd`/.rustup"
 # Ensure the build fails if it uses excessive amounts of memory.
 ulimit -d $((1024 * 1024 * 8)) # 8 GiB
 
-/usr/bin/time -v python3 x.py test --stage 2 --config .buildbot.config.toml --exclude rustdoc-json --exclude debuginfo
+ENABLE_GC_ASSERTIONS=true /usr/bin/time -v python3 x.py test --stage 2 --config .buildbot.config.toml --exclude rustdoc-json --exclude debuginfo