diff --git a/.cirrus.yml b/.cirrus.yml
index 37bb92e759..6b4f27ee2a 100644
--- a/.cirrus.yml
+++ b/.cirrus.yml
@@ -219,7 +219,7 @@ alpine_task:
 # We aim to support both the current and previous macOS release.
 macos_big_sur_task:
   macos_instance:
-    image: big-sur-base
+    image: big-sur-xcode-12.5
   prepare_script: ./ci/macos/prepare.sh
   << : *CI_TEMPLATE
   << : *MACOS_RESOURCES_TEMPLATE
diff --git a/ci/macos/prepare.sh b/ci/macos/prepare.sh
index e12bab11a5..2e81e060c3 100755
--- a/ci/macos/prepare.sh
+++ b/ci/macos/prepare.sh
@@ -5,4 +5,5 @@ sysctl hw.model hw.machine hw.ncpu hw.physicalcpu hw.logicalcpu
 set -e
 set -x
 
-brew install cmake swig openssl bison
+brew upgrade cmake openssl
+brew install swig bison