diff --git a/.github/workflows/autobuild.yml b/.github/workflows/autobuild.yml
index 9d0e600596..e25bf9dacd 100644
--- a/.github/workflows/autobuild.yml
+++ b/.github/workflows/autobuild.yml
@@ -120,7 +120,9 @@ jobs:
              target_os:             macos
              building_on_os:        macos-10.15
              cmd1_prebuild:         "./autobuild/mac/artifacts/autobuild_mac_1_prepare.sh 5.15.2"
-             cmd2_build:            "./autobuild/mac/artifacts/autobuild_mac_2_build.sh sign_if_possible"
+             # QMAKE_MAC_SDK limits the auto-used to the specified maximum version to ensure compatibility with Qt 5.15.2,
+             # QMAKE_MACOSX_DEPLOYMENT_TARGET describes the minimum version which we support with this build:
+             cmd2_build:            "env EXTRA_QMAKE_ARGS='QMAKE_MAC_SDK=macosx10.15 QMAKE_MACOSX_DEPLOYMENT_TARGET=10.13' ./autobuild/mac/artifacts/autobuild_mac_2_build.sh sign_if_possible"
              cmd3_postbuild:        "./autobuild/mac/artifacts/autobuild_mac_3_copy_files.sh"
              uses_codeql:           false
 
@@ -151,13 +153,13 @@ jobs:
     runs-on:                        ${{ matrix.config.building_on_os }}
     steps:
 
-      # For Qt5 on Mac, we need to ensure SDK 10.15 is used, and not SDK 11.x
-      # This is done by selecting Xcode 11.7 instead of the latest default of 12.x
+      # For Qt5 on Mac, we need to ensure SDK 10.15 is used.
+      # Xcode 12.0 is the last version which ships SDK 10.15, therefore pin it:
       - name:                       Select Xcode version for Mac
         if:                         ${{ matrix.config.target_os == 'macos' }}
         uses:                       maxim-lobanov/setup-xcode@v1
         with:
-          xcode-version: '11.7'
+          xcode-version: '12.4.0'
 
       # Checkout code
       - name:                       Checkout code
diff --git a/autobuild/mac/artifacts/autobuild_mac_2_build.sh b/autobuild/mac/artifacts/autobuild_mac_2_build.sh
index 8347bfe9b9..d6b14d1e85 100755
--- a/autobuild/mac/artifacts/autobuild_mac_2_build.sh
+++ b/autobuild/mac/artifacts/autobuild_mac_2_build.sh
@@ -21,6 +21,7 @@ source "$(dirname "${BASH_SOURCE[0]}")/../../ensure_THIS_JAMULUS_PROJECT_PATH.sh
 cd "${THIS_JAMULUS_PROJECT_PATH}"
 
 echo "Run deploy script..."
+export EXTRA_QMAKE_ARGS
 
 # If we have certificate details, then prepare the signing
 if [[ "${SIGN}" != "sign_if_possible" ||
@@ -47,4 +48,4 @@ else
     sh "${THIS_JAMULUS_PROJECT_PATH}"/mac/deploy_mac.sh -s "${MACOS_CERTIFICATE_ID}"
     # Set up the notarization and staple parts
     echo "::set-output name=macos_signed::true"
-fi
+fi
\ No newline at end of file
diff --git a/mac/deploy_mac.sh b/mac/deploy_mac.sh
index 438fc38a7b..f8b2c7c0dc 100755
--- a/mac/deploy_mac.sh
+++ b/mac/deploy_mac.sh
@@ -43,7 +43,7 @@ cleanup()
 build_app()
 {
     # Build Jamulus
-    qmake "${project_path}" -o "${build_path}/Makefile" "CONFIG+=release" ${@:2}
+    qmake "${project_path}" -o "${build_path}/Makefile" "CONFIG+=release" ${@:2} ${EXTRA_QMAKE_ARGS:-}
     local target_name="$(cat "${build_path}/Makefile" | sed -nE 's/^QMAKE_TARGET *= *(.*)$/\1/p')"
     local job_count="$(sysctl -n hw.ncpu)"