diff --git a/.github/workflows/autobuild.yml b/.github/workflows/autobuild.yml
index f1584198c3..786d440b14 100644
--- a/.github/workflows/autobuild.yml
+++ b/.github/workflows/autobuild.yml
@@ -237,16 +237,16 @@ jobs:
           # Reminder: If Legacy is removed, be sure to add a dedicated job for CodeQL again.
           - config_name:            MacOS Legacy (artifacts+CodeQL)
             target_os:              macos
-            building_on_os:         macos-10.15
+            building_on_os:         macos-11
             base_command:           QT_VERSION=5.9.9 SIGN_IF_POSSIBLE=0 ARTIFACT_SUFFIX=_legacy ./.github/autobuild/mac.sh
             # Enable CodeQL on mac legacy as this version does not get signed
             run_codeql:             true
             # For Qt5 on Mac, we need to ensure SDK 10.15 is used, and not SDK 11.x.
             # Xcode 12.1 is the most-recent release which still ships SDK 10.15:
             # https://developer.apple.com/support/xcode/
-            # Xcode 12.1.1 is the most-recent 12.1.x release:
-            # https://xcodereleases.com/
-            xcode_version:          12.1.1
+            # However, Github's macos-11 runner image's latest xcode version
+            # with SDK 10.15 is 11.7, so we use that.
+            xcode_version:          11.7
             is_main_build_target:   true
 
           - config_name:            iOS (artifacts)