diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 887660a..ec84603 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -8,7 +8,7 @@ jobs:
     strategy:
       matrix:
         compiler: [gcc-9, gcc-10, gcc-11, clang-12, clang-13, clang-14]
-        bits: [32, 64]
+        bits: ['32', '64']
         lto: [LTO=y, LTO=n]
 
     runs-on: 'ubuntu-22.04'
@@ -23,5 +23,5 @@ jobs:
 
     - name: make
       run: |
-        make CC=${{matrix.compiler}} M32=${{matrix.bits == 32 && 'y' || 'n'}} ${{matrix.lto}}
+        make CC=${{matrix.compiler}} BITS=${{matrix.bits}} ${{matrix.lto}}
         ./extend_skl_only.sh
diff --git a/.github/workflows/scan-build.yml b/.github/workflows/scan-build.yml
index 3ff89f4..0ebc9f1 100644
--- a/.github/workflows/scan-build.yml
+++ b/.github/workflows/scan-build.yml
@@ -7,7 +7,7 @@ jobs:
 
     strategy:
       matrix:
-        bits: [32, 64]
+        bits: ['32', '64']
         lto: [LTO=y, LTO=n]
 
     runs-on: 'ubuntu-22.04'
@@ -22,4 +22,4 @@ jobs:
 
     - name: make
       run: |
-        scan-build-14 --status-bugs -analyze-headers make M32=${{matrix.bits == 32 && 'y' || 'n'}} ${{matrix.lto}}
+        scan-build-14 --status-bugs -analyze-headers make BITS=${{matrix.bits}} ${{matrix.lto}}
diff --git a/Makefile b/Makefile
index dac53ae..f03300c 100644
--- a/Makefile
+++ b/Makefile
@@ -11,12 +11,15 @@ CFLAGS  += -flto
 LDFLAGS += -flto
 endif
 
-ifeq ($(M32),y)
+BITS ?= 64
+ifeq ($(BITS),32)
 CFLAGS  += -m32 -mregparm=3 -fno-plt -freg-struct-return
 LDFLAGS += -m32
-else
+else ifeq ($(BITS),64)
 CFLAGS  += -m64
 LDFLAGS += -m64
+else
+$(error Bad $$(BITS) value '$(BITS)')
 endif
 
 # There is a 64k total limit, so optimise for size.  The binary may be loaded