diff --git a/ci/lib.sh b/ci/lib.sh
index 288a5b3884..0c7171a173 100755
--- a/ci/lib.sh
+++ b/ci/lib.sh
@@ -163,8 +163,10 @@ linux-clang|linux-gcc)
 	export GIT_TEST_HTTPD=YesPlease
 
 	# The Linux build installs the defined dependency versions below.
-	# The OS X build installs the latest available versions. Keep that
-	# in mind when you encounter a broken OS X build!
+	# The OS X build installs much more recent versions, whichever
+	# were recorded in the Homebrew database upon creating the OS X
+	# image.
+	# Keep that in mind when you encounter a broken OS X build!
 	export LINUX_P4_VERSION="16.2"
 	export LINUX_GIT_LFS_VERSION="1.5.2"