diff --git a/.circleci/config.yml b/.circleci/config.yml
index 3863f72..f7bedfd 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -18,7 +18,7 @@ jobs:
             git submodule update --init --recursive
       # Use cached mlir installation if possible.
       - restore_cache:
-          key: V6-LLVM-PROJECT-{{ arch }}
+          key: V7-LLVM-PROJECT-{{ arch }}
       - run:
           name: Install MLIR
           command: |
@@ -29,7 +29,7 @@ jobs:
               source ONNF/utils/install-mlir.sh
             fi
       - save_cache:
-          key: V6-LLVM-PROJECT-{{ arch }}
+          key: V7-LLVM-PROJECT-{{ arch }}
           paths:
             - llvm-project
       - run:
diff --git a/utils/install-mlir.sh b/utils/install-mlir.sh
index 39f06ea..960cd19 100644
--- a/utils/install-mlir.sh
+++ b/utils/install-mlir.sh
@@ -1,4 +1,6 @@
 git clone https://github.com/llvm/llvm-project.git
+# Check out a specific branch that is known to work with ONNF.
+cd llvm-project && git checkout 391cc4dd41db934081c37ee523cb2149bf0e3a41 && cd ..
 mkdir llvm-project/build
 cd llvm-project/build
 cmake -G Ninja ../llvm \