diff --git a/mps/.travis.yml b/mps/.travis.yml
index 30c85c5c410..883617763c1 100644
--- a/mps/.travis.yml
+++ b/mps/.travis.yml
@@ -5,6 +5,9 @@ language: c
 os:
   - linux
   - osx
+arch:
+  - amd64
+  - arm64
 compiler:
   - clang
   - gcc
@@ -12,6 +15,10 @@ matrix:
   exclude:
     - os: osx
       compiler: gcc
+  exclude:
+    - os: linux
+      arch: arm64
+      compiler: gcc
 notifications:
   email:
     - mps-travis@ravenbrook.com
diff --git a/mps/code/.p4ignore b/mps/code/.p4ignore
index 682821ffd84..7ac128137a3 100644
--- a/mps/code/.p4ignore
+++ b/mps/code/.p4ignore
@@ -8,6 +8,7 @@ fri3gc
 fri3ll
 fri6gc
 fri6ll
+lia6ll
 lii3gc
 lii6gc
 lii6ll
diff --git a/mps/code/lia6ll.gmk b/mps/code/lia6ll.gmk
new file mode 100644
index 00000000000..9e329ee98a4
--- /dev/null
+++ b/mps/code/lia6ll.gmk
@@ -0,0 +1,55 @@
+# -*- makefile -*-
+#
+# lia6ll.gmk: BUILD FOR LINUX/ARM64/Clang PLATFORM
+#
+# $Id$
+# Copyright (c) 2001-2021 Ravenbrook Limited.  See end of file for license.
+
+PFM = lia6ll
+
+MPMPF = \
+    lockix.c \
+    prmcanan.c \
+    prmcix.c \
+    prmclia6.c \
+    protix.c \
+    protsgix.c \
+    pthrdext.c \
+    span.c \
+    thix.c \
+    vmix.c
+
+LIBS = -lm -lpthread
+
+include ll.gmk
+include comm.gmk
+
+
+# C. COPYRIGHT AND LICENSE
+#
+# Copyright (C) 2001-2021 Ravenbrook Limited <https://www.ravenbrook.com/>.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+#
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the
+#    distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
diff --git a/mps/code/ll.gmk b/mps/code/ll.gmk
index ce1db14aef8..16ebf0e7874 100644
--- a/mps/code/ll.gmk
+++ b/mps/code/ll.gmk
@@ -14,11 +14,11 @@ CFLAGSDEBUG = -O0 -g3
 CFLAGSOPT = -O2 -g3
 
 # Warnings that might be enabled by clients <design/config/#.warning.impl>.
+# TODO: add -Wcomma when all our continuous integration platforms support it.
 CFLAGSCOMPILER := \
 	-Waggregate-return \
 	-Wall \
 	-Wcast-qual \
-	-Wcomma \
 	-Wconversion \
 	-Wduplicate-enum \
 	-Werror \
diff --git a/mps/code/mps.c b/mps/code/mps.c
index 3fbfc579f7e..543b40166c8 100644
--- a/mps/code/mps.c
+++ b/mps/code/mps.c
@@ -182,6 +182,21 @@
 #include "prmcfri6.c"   /* x86-64 for FreeBSD mutator context */
 #include "span.c"       /* generic stack probe */
 
+/* Linux on ARM64 with Clang */
+
+#elif defined(MPS_PF_LIA6LL)
+
+#include "lockix.c"     /* Posix locks */
+#include "thix.c"       /* Posix threading */
+#include "pthrdext.c"   /* Posix thread extensions */
+#include "vmix.c"       /* Posix virtual memory */
+#include "protix.c"     /* Posix protection */
+#include "protsgix.c"   /* Posix signal handling */
+#include "prmcanan.c"   /* generic architecture mutator context */
+#include "prmcix.c"     /* Posix mutator context */
+#include "prmclia6.c"   /* x86-64 for Linux mutator context */
+#include "span.c"       /* generic stack probe */
+
 /* Linux on IA-32 with GCC */
 
 #elif defined(MPS_PF_LII3GC)
diff --git a/mps/code/mpstd.h b/mps/code/mpstd.h
index df56d29f2a6..f836efdb56d 100644
--- a/mps/code/mpstd.h
+++ b/mps/code/mpstd.h
@@ -222,6 +222,25 @@
 #define MPS_PF_ALIGN    8
 
 
+/* Clang/LLVM 10.0, clang -E -dM */
+
+#elif defined(__linux__) && defined(__aarch64__) && defined(__GNUC__) \
+      && defined(__clang__)
+#if defined(CONFIG_PF_STRING) && ! defined(CONFIG_PF_LIA6LL)
+#error "specified CONFIG_PF_... inconsistent with detected lia6ll"
+#endif
+#define MPS_PF_LIA6LL
+#define MPS_PF_STRING   "lia6ll"
+#define MPS_OS_LI
+#define MPS_ARCH_A6
+#define MPS_BUILD_LL
+#define MPS_T_WORD      unsigned long
+#define MPS_T_ULONGEST  unsigned long
+#define MPS_WORD_WIDTH  64
+#define MPS_WORD_SHIFT  6
+#define MPS_PF_ALIGN    8
+
+
 /* GCC 2.6.3, gcc -E -dM
  * The actual granularity of GNU malloc is 8, but field alignments are
  * all 4.
diff --git a/mps/code/prmclia6.c b/mps/code/prmclia6.c
new file mode 100644
index 00000000000..b79bb9db48c
--- /dev/null
+++ b/mps/code/prmclia6.c
@@ -0,0 +1,53 @@
+/* prmclia6.c: MUTATOR CONTEXT ARM64 (LINUX)
+ *
+ * $Id$
+ * Copyright (c) 2001-2021 Ravenbrook Limited.  See end of file for license.
+ *
+ * .purpose: Implement the mutator context module. <design/prmc>.
+ */
+
+#include "prmcix.h"
+
+SRCID(prmclia6, "$Id$");
+
+#if !defined(MPS_OS_LI) || !defined(MPS_ARCH_A6)
+#error "prmclia6.c is specific to MPS_OS_LI and MPS_ARCH_A6"
+#endif
+
+
+Addr MutatorContextSP(MutatorContext context)
+{
+  AVERT(MutatorContext, context);
+
+  return (Addr)context->ucontext->uc_mcontext.sp;
+}
+
+
+/* C. COPYRIGHT AND LICENSE
+ *
+ * Copyright (C) 2001-2021 Ravenbrook Limited <https://www.ravenbrook.com/>.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+ * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
diff --git a/mps/configure b/mps/configure
index cb018412424..fefd2a0051a 100755
--- a/mps/configure
+++ b/mps/configure
@@ -3454,6 +3454,14 @@ CLEAN_TARGET=clean-make-build
 INSTALL_TARGET=install-make-build
 TEST_TARGET=test-make-build
 case $host/$CLANG in
+  aarch64-*-linux*/yes)
+      { $as_echo "$as_me:${as_lineno-$LINENO}: result: Linux ARM64" >&5
+$as_echo "Linux ARM64" >&6; }
+      MPS_OS_NAME=li
+      MPS_ARCH_NAME=a6
+      MPS_BUILD_NAME=ll
+      PFMCFLAGS="$CFLAGS_LL"
+    ;;
   i*86-*-linux*/no)
       { $as_echo "$as_me:${as_lineno-$LINENO}: result: Linux x86" >&5
 $as_echo "Linux x86" >&6; }
diff --git a/mps/configure.ac b/mps/configure.ac
index acf935b640e..fbf19cec06e 100644
--- a/mps/configure.ac
+++ b/mps/configure.ac
@@ -45,6 +45,13 @@ CLEAN_TARGET=clean-make-build
 INSTALL_TARGET=install-make-build
 TEST_TARGET=test-make-build
 case $host/$CLANG in
+  aarch64-*-linux*/yes)
+      AC_MSG_RESULT([Linux ARM64])
+      MPS_OS_NAME=li
+      MPS_ARCH_NAME=a6
+      MPS_BUILD_NAME=ll
+      PFMCFLAGS="$CFLAGS_LL"
+    ;;
   i*86-*-linux*/no)
       AC_MSG_RESULT([Linux x86])
       MPS_OS_NAME=li
diff --git a/mps/design/prmc.txt b/mps/design/prmc.txt
index fb141f23a8c..6c55634a8b0 100644
--- a/mps/design/prmc.txt
+++ b/mps/design/prmc.txt
@@ -178,8 +178,8 @@ Posix implementation
 
 _`.impl.ix`: In ``prmcix.c`` and ``protsgix.c``, with
 processor-specific parts in ``prmci3.c`` and ``prmci6.c``, and other
-platform-specific parts in ``prmcfri3.c``, ``prmclii3.c``,
-``prmcfri6.c``, and ``prmclii6.c``.
+platform-specific parts in ``prmcfri3.c``, ``prmcfri6.c``,
+``prmclia6.c``, ``prmclii3.c``, and ``prmclii6.c``.
 
 _`.impl.ix.context`: The context consists of the |siginfo_t|_ and
 |ucontext_t|_ structures. POSIX specifies some of the fields in
diff --git a/mps/manual/build.txt b/mps/manual/build.txt
index 8a5e55c1795..7f7f8813f81 100644
--- a/mps/manual/build.txt
+++ b/mps/manual/build.txt
@@ -139,6 +139,7 @@ Platform     OS          Architecture    Compiler      Makefile
 ``fri3ll``   FreeBSD     IA-32           Clang         ``fri3ll.gmk``
 ``fri6gc``   FreeBSD     x86-64          GCC           ``fri6gc.gmk``
 ``fri6ll``   FreeBSD     x86-64          Clang         ``fri6ll.gmk``
+``lia6ll``   Linux       ARM64           Clang         ``lia6ll.gmk``
 ``lii3gc``   Linux       IA-32           GCC           ``lii3gc.gmk``
 ``lii6gc``   Linux       x86-64          GCC           ``lii6gc.gmk``
 ``lii6ll``   Linux       x86-64          Clang         ``lii6ll.gmk``
diff --git a/mps/manual/source/code-index.rst b/mps/manual/source/code-index.rst
index f30ac3a1e59..3fc9530cf5c 100644
--- a/mps/manual/source/code-index.rst
+++ b/mps/manual/source/code-index.rst
@@ -175,6 +175,7 @@ prmci6.c      Mutator context implementation for x86-64.
 prmci6.h      Mutator context interface for x86-64.
 prmcix.c      Mutator context implementation for POSIX.
 prmcix.h      Mutator context interface for POSIX.
+prmclia6.c    Mutator context implementation for Linux, ARM64.
 prmclii3.c    Mutator context implementation for Linux, IA-32.
 prmclii6.c    Mutator context implementation for Linux, x86-64.
 prmcw3.c      Mutator context implementation for Windows.
@@ -384,6 +385,7 @@ fri6gc.gmk     GNU makefile for platform FRI6GC.
 fri6ll.gmk     GNU makefile for platform FRI6LL.
 gc.gmk         GNU make fragment for GCC.
 gp.gmk         GNU make fragment for GCC/GProf (broken).
+lia6ll.gmk     GNU makefile for platform LIA6LL.
 lii3gc.gmk     GNU makefile for platform LII3GC.
 lii6gc.gmk     GNU makefile for platform LII6GC.
 lii6ll.gmk     GNU makefile for platform LII6LL.
diff --git a/mps/manual/source/release.rst b/mps/manual/source/release.rst
index 70d5b7ccded..167af1bec87 100644
--- a/mps/manual/source/release.rst
+++ b/mps/manual/source/release.rst
@@ -12,7 +12,10 @@ Release 1.118.0
 New features
 ............
 
-#. New supported platform ``xca6ll`` (macOS, ARM64, Clang/LLVM).
+#. New supported platforms:
+
+   * ``lia6ll`` (Linux, ARM64, Clang/LLVM).
+   * ``xca6ll`` (macOS, ARM64, Clang/LLVM).
 
 #. The MPS no longer supports building for the xci3ll platform (macOS,
    IA-32, Clang/LLVM) using Xcode. This is because Xcode 10.0 no
diff --git a/mps/manual/source/topic/platform.rst b/mps/manual/source/topic/platform.rst
index d72f3fb7a28..72ecedc8d39 100644
--- a/mps/manual/source/topic/platform.rst
+++ b/mps/manual/source/topic/platform.rst
@@ -171,6 +171,13 @@ Platform interface
     x86-64 processor architecture, and the Clang/LLVM compiler.
 
 
+.. c:macro:: MPS_PF_LIA6LL
+
+    A :term:`C` preprocessor macro that indicates, if defined, that
+    the :term:`platform` consists of the Linux operating system, the
+    ARM64 processor architecture, and the Clang/LLVM compiler.
+
+
 .. c:macro:: MPS_PF_LII3GC
 
     A :term:`C` preprocessor macro that indicates, if defined, that
@@ -370,6 +377,7 @@ Platform    Status
 ``fri6ll``  Supported
 ``i5m2cc``  *Not supported*
 ``iam4cc``  *Not supported*
+``lia6ll``  Supported
 ``lii3eg``  *Not supported*
 ``lii3gc``  Supported
 ``lii4gc``  Corrected to ``lii3gc``
diff --git a/mps/manual/source/topic/porting.rst b/mps/manual/source/topic/porting.rst
index 30e039d9627..87cdf95e06c 100644
--- a/mps/manual/source/topic/porting.rst
+++ b/mps/manual/source/topic/porting.rst
@@ -76,8 +76,9 @@ usable.
    stack` can be scanned.
 
    See :ref:`design-prmc` for the design, and ``prmc.h`` for the
-   interface. There are implementations on Unix and Windows for
-   IA-32 and x86-64, and on macOS for IA-32, x86-64, and ARM64.
+   interface. There are implementations on FreeBSD and Windows for
+   IA-32 and x86-64, and on Linux and macOS for IA-32, x86-64, and
+   ARM64.
 
    There is a generic implementation in ``prmcan.c``, which can't
    provide these features, and so only supports a single thread.