diff --git a/.github/workflows/macos-gcc.yml b/.github/workflows/macos-gcc.yml
index e4821dc..8e47f23 100644
--- a/.github/workflows/macos-gcc.yml
+++ b/.github/workflows/macos-gcc.yml
@@ -40,7 +40,7 @@ jobs:
 
     - name: Build
       run: |
-        make ARCH=${{ matrix.arch }} CROSS_COMPILE=${{ matrix.cross_compile }} USING_APPLE=1
+        make ARCH=${{ matrix.arch }} CROSS_COMPILE=${{ matrix.cross_compile }}
     
     - name: Generate binary information
       run: ${{ matrix.cross_compile }}readelf -a ./${{ matrix.dir }}/apps/ctors_dtors_priority_test.so > ./${{ matrix.dir }}/apps/readelf.txt
diff --git a/Make.defaults b/Make.defaults
index 7ef3ea2..221e157 100755
--- a/Make.defaults
+++ b/Make.defaults
@@ -110,7 +110,7 @@ endif
 GCCVERSION   := $(shell $(CC) -dumpversion | sed -e 's/-win32/.0/' | cut -f1 -d.)
 GCCMINOR     := $(shell $(CC) -dumpversion | sed -e 's/-win32/.0/' | cut -f2 -d.)
 USING_CLANG  := $(shell $(CC) -v 2>&1 | grep -q 'clang version' && echo clang || echo 0)
-USING_APPLE  ?= 0
+USING_APPLE  ?= $(shell uname -s | grep -q 'Darwin' && echo 1 || echo 0)
 
 # Rely on GCC MS ABI support?
 GCCNEWENOUGH := $(shell ( [ $(GCCVERSION) -gt "4" ]           \
diff --git a/inc/efi.h b/inc/efi.h
index cec1569..3c426c1 100644
--- a/inc/efi.h
+++ b/inc/efi.h
@@ -37,6 +37,10 @@ Revision History
 extern "C" {
 #endif
 
+#if defined(__APPLE__)
+#error "Mach-O toolchain isn't supported; please compile with an ELF toolchain from Homebrew"
+#endif
+
 #define EFI_FIRMWARE_VENDOR         L"INTEL"
 #define EFI_FIRMWARE_MAJOR_REVISION 12
 #define EFI_FIRMWARE_MINOR_REVISION 33
diff --git a/inc/subst/elf.h b/inc/subst/elf.h
index 7004996..f39fe96 100644
--- a/inc/subst/elf.h
+++ b/inc/subst/elf.h
@@ -11,7 +11,7 @@ You should have received a copy of the GNU Lesser General Public License along w
 if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
-#if !defined(__APPLE__) && !defined(__GNU_EFI_IS_APPLE)
+#if !defined(__GNU_EFI_IS_APPLE)
 #include <elf.h>
 
 #else