diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 9e9b0b6..b7e6db9 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -68,6 +68,10 @@ jobs:
     name: Compile (MacOS clang, aarch64)
     needs: [ dist ]
     runs-on: macOS-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        feature: [ enable-aarch64, disable-aarch64 ]
     steps:
     - name: Download source package artifact
       uses: actions/download-artifact@v4
@@ -76,7 +80,7 @@ jobs:
     - name: Extract source package
       run: tar --strip-components=1 -xf xpar-${{ github.sha }}.tar.gz
     - name: Configure
-      run: ./configure CC=clang
+      run: ./configure CC=clang --${{ matrix.feature }}
     - name: Make
       run: make all self-check
   
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 4b3914e..e2ee976 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -52,8 +52,8 @@ jobs:
       fail-fast: false
       matrix:
         target:
-          - [ "x86_64-linux", "--enable-static --enable-lto", "" ]
-          - [ "x86_64", "CC=x86_64-w64-mingw32-gcc --host x86_64-w64-mingw32 --enable-static --enable-lto", "gcc-mingw-w64-x86-64" ]
+          - [ "x86_64-linux", "--enable-static --enable-lto --enable-x86-64", "" ]
+          - [ "x86_64", "CC=x86_64-w64-mingw32-gcc --host x86_64-w64-mingw32 --enable-static --enable-lto --enable-x86-64", "gcc-mingw-w64-x86-64" ]
           - [ "i686", "CC=i686-w64-mingw32-gcc --host i686-w64-mingw32 --enable-static --enable-lto", "gcc-mingw-w64-i686" ]
     steps:
       - name: Download source package artifact
diff --git a/Makefile.am b/Makefile.am
index ced1432..9206978 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -10,6 +10,10 @@ SUFFIXES = .asm
 	$(NASM) $(NAFLAGS) -o $@ $<
 endif
 
+if XPAR_AARCH64
+xpar_SOURCES += xpar-aarch64.S
+endif
+
 # Developer convenience targets
 .PHONY: update-ChangeLog
 update-ChangeLog:
diff --git a/README.md b/README.md
index 12e11c2..fc8735f 100644
--- a/README.md
+++ b/README.md
@@ -38,14 +38,11 @@ A rough outline of some development-related topics below.
 ## Roadmap
 
 - Need to implement the parallel variant.
-- Need to provide automatic testing for all configurations.
 - Write a proper readme, manpages, etc.
-- Make sure that this builds on Windows and port over the assembly code.
-- Fuzz to find segfaults.
-- Apple M1-specific optimizations to CRC32.
 - 32- vs 64-bit code: determine if there's any compatibility issues.
 
 Low priority:
+- Speed up the joint mode encoder loop (basically a LFSR).
 - Should probably not pad to the full interlacing block size.
 - Add assembly routines for hot spots in the program.
 
@@ -61,8 +58,3 @@ As it stands:
 
 Code style:
 - Two space indent, brace on the same line, middle pointers - `char * p;`.
-
-## Show-stoppers
-
-clang bug (msys2 packages repository ticket 4958) - makes it impossible to
-build on x86_64 Windows with clang. Only gcc is supported.
diff --git a/configure.ac b/configure.ac
index 33d4c41..5baaeea 100644
--- a/configure.ac
+++ b/configure.ac
@@ -15,6 +15,7 @@ AM_INIT_AUTOMAKE([-Wall color-tests])
 AC_PROG_INSTALL
 AC_PROG_MAKE_SET
 AC_PROG_CC
+AM_PROG_AS
 
 AC_CHECK_HEADERS([getopt.h io.h])
 AC_CHECK_FUNCS([getopt_long asprintf strndup stat _commit _setmode isatty fsync mmap CreateFileMappingA])
@@ -34,6 +35,14 @@ else
   AM_CONDITIONAL([XPAR_X86_64], [false])
 fi
 
+AC_ARG_ENABLE([aarch64], [AS_HELP_STRING([--enable-aarch64], [Enable aarch64 platform specific code.])], [enable_aarch64=$enableval], [enable_aarch64=no])
+if test "x$enable_aarch64" = "xyes"; then
+  AC_DEFINE([XPAR_AARCH64], [1], [Enable aarch64 platform specific code.])
+  AM_CONDITIONAL([XPAR_AARCH64], [true])
+else
+  AM_CONDITIONAL([XPAR_AARCH64], [false])
+fi
+
 AC_ARG_ENABLE([native], [AS_HELP_STRING([--enable-native], [Enable native platform optimisations.])], [enable_native=$enableval], [enable_native=no])
 if test "x$enable_native" = "xyes"; then
   AX_APPEND_COMPILE_FLAGS([-march=native -mtune=native])
diff --git a/crc32c.c b/crc32c.c
index 047d850..fa1776b 100644
--- a/crc32c.c
+++ b/crc32c.c
@@ -89,26 +89,36 @@ u32 crc32c_tabular(u32 crc, u8 * data, sz length) {
   return crc;
 }
 
+typedef u32 (*crc32c_func)(u32, u8 *, sz);
+
 #if defined(XPAR_X86_64)
   #ifdef HAVE_FUNC_ATTRIBUTE_SYSV_ABI
     #define EXTERNAL_ABI __attribute__((sysv_abi))
   #else
     #define EXTERNAL_ABI
   #endif
-  
-  typedef u32 (*crc32c_func)(u32, u8 *, sz);
+
   extern EXTERNAL_ABI int crc32c_x86_64_cpuflags(void);
   extern EXTERNAL_ABI u32 crc32c_small_x86_64_sse42(u32, u8 *, sz);
+#elif defined(XPAR_AARCH64)
+  extern int crc32c_aarch64_cpuflags(void);
+  extern u32 crc32c_small_aarch64_neon(u32, u8 *, sz);
 #endif
 
 u32 crc32c(u8 * data, sz length) {
-#if defined(XPAR_X86_64)
   static int cpuflags = -1;
+#if defined(XPAR_X86_64)
   if (cpuflags == -1) cpuflags = crc32c_x86_64_cpuflags();
   if (cpuflags & 1)
     return crc32c_small_x86_64_sse42(0xFFFFFFFFL, data, length) ^ 0xFFFFFFFFL;
   else
     return crc32c_tabular(0xFFFFFFFFL, data, length) ^ 0xFFFFFFFFL;
+#elif defined(XPAR_AARCH64)
+  if (cpuflags == -1) cpuflags = crc32c_aarch64_cpuflags();
+  if (cpuflags)
+    return crc32c_small_aarch64_neon(0xFFFFFFFFL, data, length) ^ 0xFFFFFFFFL;
+  else
+    return crc32c_tabular(0xFFFFFFFFL, data, length) ^ 0xFFFFFFFFL;
 #else
   return crc32c_tabular(0xFFFFFFFFL, data, length) ^ 0xFFFFFFFFL;
 #endif
diff --git a/xpar-aarch64.S b/xpar-aarch64.S
new file mode 100644
index 0000000..eed513c
--- /dev/null
+++ b/xpar-aarch64.S
@@ -0,0 +1,120 @@
+/*
+  Copyright (C) 2022-2024 Kamila Szewczyk
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation; either version 3 of the License, or
+  (at your option) any later version.
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+  You should have received a copy of the GNU General Public License
+  along with this program. If not, see <http://www.gnu.org/licenses/>.
+*/
+
+.text
+.extern getauxval
+
+#if defined(__APPLE__)
+; aarch64 MacOS
+.extern _sysctlbyname
+.globl _crc32c_aarch64_cpuflags
+_crc32c_aarch64_cpuflags:
+  sub sp, sp, #32
+  stp x29, x30, [sp, #16]
+  add x29, sp, #16
+  mov w8, #4
+  adrp x0, .name@GOTPAGE
+  ldr x0, [x0, .name@GOTPAGEOFF]
+  sub x1, x29, #4
+  mov x2, sp
+  mov x3, xzr
+  mov x4, xzr
+  stur wzr, [x29, #-4]
+  str x8, [sp]
+  bl _sysctlbyname
+  ldur w8, [x29, #-4]
+  cmp w0, #0
+  ccmp w8, #0, #4, eq
+  cset w0, ne
+  ldp x29, x30, [sp, #16]
+  add sp, sp, #32
+  ret
+.name: .asciz "hw.optional.armv8_crc32"
+#else
+; aarch64 Linux
+.extern getauxval
+.globl crc32c_aarch64_cpuflags
+crc32c_aarch64_cpuflags:
+  stp x29, x30, [sp, -16]!
+  mov x0, 16 ; AT_HWCAP
+  mov x29, sp
+  bl getauxval
+  ldp x29, x30, [sp], 16
+  and w0, w0, 128
+  ret
+#endif
+
+/* Uses fundamentally the same algorithm as crc32c_small_x86_64_sse42 */
+
+#if defined(__APPLE__)
+.globl _crc32c_small_aarch64_neon
+_crc32c_small_aarch64_neon:
+#else
+.globl crc32c_small_aarch64_neon
+crc32c_small_aarch64_neon:
+#endif
+  cmp x2, 63
+  bls .fallback_1way
+  sub x8, x2, #64
+  mov x3, x1
+  and x7, x8, -64
+  add x7, x7, 64
+  add x7, x1, x7
+.crc32c_8way_quad:
+  ldp x4, x6, [x3]
+  crc32cx w0, w0, x4
+  ldp x4, x5, [x3, 16]
+  crc32cx w0, w0, x6
+  crc32cx w0, w0, x4
+  ldp x4, x6, [x3, 32]
+  crc32cx w0, w0, x5
+  crc32cx w0, w0, x4
+  ldp x5, x4, [x3, 48]
+  crc32cx w0, w0, x6
+  add x3, x3, 64
+  crc32cx w0, w0, x5
+  crc32cx w0, w0, x4
+  cmp x3, x7
+  bne .crc32c_8way_quad
+  and x8, x8, -64
+  add x1, x1, 64
+  add x1, x8, x1
+  and x2, x2, 63
+.fallback_1way:
+  cmp x2, 7
+  bls .fallback_1way_byte
+  sub x6, x2, #8
+  mov x3, x1
+  lsr x5, x6, 3
+  add w5, w5, 1
+  add x5, x1, x5, lsl 3
+.crc32c_1way_quad:
+  ldr x4, [x3], 8
+  crc32cx w0, w0, x4
+  cmp x3, x5
+  bne .crc32c_1way_quad
+  and x6, x6, -8
+  add x1, x1, 8
+  add x1, x6, x1
+  and x2, x2, 7
+.fallback_1way_byte:
+  cbz x2, .crc32c_done
+  add x2, x1, x2
+.crc32c_1way_byte:
+  ldrb    w3, [x1], 1
+  crc32cb w0, w0, w3
+  cmp x1, x2
+  bne .crc32c_1way_byte
+.crc32c_done:
+  ret
\ No newline at end of file