diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 26409d6..8ce6fce 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -37,6 +37,42 @@ jobs:
           name: gsplus-macos
           path: build/*.dmg
 
+  macos-universal:
+    # Second macOS build producing a UNIVERSAL (arm64 + x86_64) app, alongside
+    # the arm64-only `macos` job above. Key difference: we do NOT install
+    # Homebrew's SDL3 (it ships a single-arch arm64 dylib you can't link into a
+    # universal binary). With no system SDL3, CMake's FetchContent path builds
+    # SDL3 from source, and CMAKE_OSX_ARCHITECTURES makes that build -- and ours
+    # -- universal. fixup_bundle then embeds the universal SDL3 into the .app.
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install tools
+        # NB: intentionally no `sdl3` here -- see the comment above.
+        run: brew install cmake ninja
+      - name: Configure (universal, SDL3 built from source)
+        run: |
+          ARGS=""
+          case "$GITHUB_REF" in
+            refs/tags/v*) ARGS="-DGSPLUS_VERSION=${GITHUB_REF_NAME#v}" ;;
+          esac
+          cmake -G Ninja -B build -S gsplus/src \
+            -DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" $ARGS
+      - name: Build
+        run: cmake --build build --target gsplus-sdl
+      - name: Package (.dmg) and label universal
+        run: |
+          cd build && cpack
+          # CPack names it GSplus-<ver>-Darwin.dmg; rename so it doesn't collide
+          # with the arm64-only dmg when both attach to the same Release.
+          for f in GSplus-*-Darwin.dmg; do
+            mv "$f" "${f/-Darwin.dmg/-macOS-universal.dmg}"
+          done
+      - uses: actions/upload-artifact@v4
+        with:
+          name: gsplus-macos-universal
+          path: build/*.dmg
+
   linux:
     runs-on: ubuntu-latest
     steps:
@@ -105,7 +141,7 @@ jobs:
 
   release:
     if: startsWith(github.ref, 'refs/tags/')
-    needs: [ macos, linux, windows ]
+    needs: [ macos, macos-universal, linux, windows ]
     runs-on: ubuntu-latest
     permissions:
       contents: write          # required for the token to create a Release
diff --git a/gsplus/src/CMakeLists.txt b/gsplus/src/CMakeLists.txt
index ab8558c..ebb0cea 100644
--- a/gsplus/src/CMakeLists.txt
+++ b/gsplus/src/CMakeLists.txt
@@ -149,7 +149,18 @@ message(STATUS "GSplus: configured core library (build type: ${CMAKE_BUILD_TYPE}
 #  Swift runtime linking / rpaths automatically, which is the fragile part the
 #  Makefile does by hand.
 # ----------------------------------------------------------------------------
-if(APPLE)
+# CMake's Swift support can't build a universal (multi-arch) binary -- it errors
+# with "multiple values for CMAKE_OSX_ARCHITECTURES not supported with Swift".
+# The native Cocoa app is legacy/secondary and excluded from the default build,
+# so when a universal build is requested (the CI macos-universal job passes
+# arm64;x86_64) we simply skip it; the shipped SDL app (gsplus-sdl, plain C) has
+# no such restriction and still builds universal.
+list(LENGTH CMAKE_OSX_ARCHITECTURES _gsplus_narch)
+if(APPLE AND _gsplus_narch GREATER 1)
+    message(STATUS "GSplus: universal build -- skipping the Swift Cocoa app (Swift can't do multi-arch)")
+endif()
+
+if(APPLE AND _gsplus_narch LESS 2)
     # Turn on CMake's Swift language support. This makes CMake able to compile
     # .swift files and, when it links a target that contains Swift, pull in the
     # Swift runtime and set rpaths for us.
@@ -258,6 +269,11 @@ target_link_libraries(gsplus-sdl PRIVATE gsplus_core_sdl SDL3::SDL3)
 if(APPLE)
     # macOS-only: retune SDL's default menu bar so ⌘ combos pass through to the
     # emulated IIgs and GSplus quits on ⌥⌘Q. The Objective-C source needs Cocoa.
+    # Explicitly enable the OBJC language so CMake has a proper compile rule for
+    # the .m file. A single-arch build tolerates compiling it via the C rule, but
+    # a universal build (CMAKE_OSX_ARCHITECTURES=arm64;x86_64) errors with
+    # "CMAKE_OBJC_COMPILE_OBJECT not set" unless OBJC is enabled.
+    enable_language(OBJC)
     target_sources(gsplus-sdl PRIVATE sdl_mac_menu.m)
     target_link_libraries(gsplus-sdl PRIVATE "-framework Cocoa")
 endif()
@@ -346,12 +362,18 @@ if(APPLE)
     # bundle. We then re-sign ad-hoc ("-"): editing a binary invalidates its
     # code signature, and arm64 macOS refuses to launch a broken-signature app.
     install(TARGETS gsplus-sdl BUNDLE DESTINATION .)
-    install(CODE [[
+    # Tell fixup_bundle which directory to search for @rpath-named dylibs. A
+    # Homebrew SDL3 records an absolute/resolvable install name, but a
+    # FetchContent-built SDL3 (the universal job, and any host without system
+    # SDL3) names itself @rpath/libSDL3.0.dylib -- fixup_bundle can't find that
+    # unless we hand it the directory containing the built dylib. The genex
+    # resolves to Homebrew's libdir or the FetchContent build dir as appropriate.
+    install(CODE "
         include(BundleUtilities)
-        fixup_bundle("${CMAKE_INSTALL_PREFIX}/GSplus.app" "" "")
+        fixup_bundle(\"\${CMAKE_INSTALL_PREFIX}/GSplus.app\" \"\" \"$<TARGET_FILE_DIR:SDL3::SDL3>\")
         execute_process(COMMAND codesign --force --deep --sign -
-            "${CMAKE_INSTALL_PREFIX}/GSplus.app")
-    ]])
+            \"\${CMAKE_INSTALL_PREFIX}/GSplus.app\")
+    ")
     set(CPACK_GENERATOR "DragNDrop")          # -> a .dmg
     set(CPACK_DMG_VOLUME_NAME "GSplus")
 else()