diff --git a/ports/unix/Makefile b/ports/unix/Makefile
index d5bd6d4098..9a9df82629 100644
--- a/ports/unix/Makefile
+++ b/ports/unix/Makefile
@@ -103,7 +103,7 @@ CC = clang
 endif
 # Use clang syntax for map file
 LDFLAGS_ARCH = -Wl,-map,$@.map -Wl,-dead_strip
-else
+else ifeq ($(UNAME_S),Linux)
 # Use gcc syntax for map file
 LDFLAGS_ARCH = -Wl,-Map=$@.map,--cref -Wl,--gc-sections
 endif
diff --git a/ports/unix/build-wasi.sh b/ports/unix/build-wasi.sh
new file mode 100755
index 0000000000..9a99fca3c9
--- /dev/null
+++ b/ports/unix/build-wasi.sh
@@ -0,0 +1,54 @@
+#! /bin/sh
+
+# prerequisites
+#
+# https://github.com/WebAssembly/wasi-libc/pull/483 (wasi-sdk 22.0?)
+# https://github.com/WebAssembly/wasi-libc/pull/473 (wasi-sdk 22.0?)
+# https://github.com/WebAssembly/binaryen/pull/6294 (version_117)
+# https://github.com/WebAssembly/binaryen/pull/6259 (version_117)
+# https://github.com/llvm/llvm-project/pull/84137 (LLVM 19?)
+#
+# WASI_SDK: wasi-sdk 21.0
+# WASM_OPT: binaryen wasm-opt built with the above patches
+# WASI_SYSROOT: wasi-libc built with the above patches
+# CLANG: clang built with the above patches
+
+WASI_SDK=${WASI_SDK:-/opt/wasi-sdk-21.0}
+WASI_SYSROOT=${WASI_SYSROOT:-${HOME}/git/wasi-libc/sysroot}
+BINARYEN_BIN=${BINARYEN_BIN:-${HOME}/git/wasm/binaryen/b/bin}
+WASM_OPT=${WASM_OPT:-${BINARYEN_BIN}/wasm-opt}
+RESOURCE_DIR=$(${WASI_SDK}/bin/clang --print-resource-dir)
+LLVM_BUILD_DIR=${LLVM_BUILD_DIR:-/Volumes/PortableSSD/llvm/build}
+CLANG=${CLANG:-${LLVM_BUILD_DIR}/bin/clang}
+CC="${CLANG} --sysroot ${WASI_SYSROOT} -resource-dir ${RESOURCE_DIR}"
+
+CFLAGS="-D_WASI_EMULATED_PROCESS_CLOCKS -D_WASI_EMULATED_SIGNAL -D_WASI_EMULATED_MMAN -mllvm -wasm-enable-sjlj" \
+LDFLAGS="-lwasi-emulated-process-clocks -lwasi-emulated-signal -lwasi-emulated-mman -lsetjmp" \
+make \
+CC="${CC}" \
+LD="${WASI_SDK}/bin/wasm-ld" \
+STRIP="${WASI_SDK}/bin/strip" \
+SIZE="${WASI_SDK}/bin/size" \
+UNAME_S=wasi \
+VARIANT=wasi \
+"$@"
+
+PROG=build-wasi/micropython
+
+# We doesn't have a way to scan GC roots like WASM locals.
+# Hopefully --spill-pointers can workaround it.
+${WASM_OPT} \
+--spill-pointers \
+-o ${PROG}.spilled ${PROG}
+
+# LLVM still uses the older version of EH proposal.
+# Convert to the latest version of EH proposal.
+${WASM_OPT} \
+--translate-to-new-eh --enable-exception-handling \
+-o ${PROG}.spilled.neweh ${PROG}.spilled
+
+# now you can run it with EH-enabled runtimes.
+# eg.  (using the latest EH)
+# toywasm --wasi build-wasi/micropython.spilled.neweh
+# eg.  (using the old EH)
+# iwasm build-wasi/micropython.spilled
diff --git a/ports/unix/mpconfigport.h b/ports/unix/mpconfigport.h
index 1086baea06..3265ca84e8 100644
--- a/ports/unix/mpconfigport.h
+++ b/ports/unix/mpconfigport.h
@@ -155,7 +155,9 @@ typedef long mp_off_t;
 #define MICROPY_PY_SYS_PATH_ARGV_DEFAULTS (0)
 
 // Enable sys.executable.
+#ifndef MICROPY_PY_SYS_EXECUTABLE
 #define MICROPY_PY_SYS_EXECUTABLE (1)
+#endif
 
 #define MICROPY_PY_SOCKET_LISTEN_BACKLOG_DEFAULT (SOMAXCONN < 128 ? SOMAXCONN : 128)
 
diff --git a/ports/unix/unix_mphal.c b/ports/unix/unix_mphal.c
index 5f5abc2e05..3ea3107d54 100644
--- a/ports/unix/unix_mphal.c
+++ b/ports/unix/unix_mphal.c
@@ -43,7 +43,13 @@
 #endif
 #endif
 
-#ifndef _WIN32
+#if defined(_WIN32) || defined(__wasi__)
+#define HAS_SIGNAL 0
+#else
+#define HAS_SIGNAL 1
+#endif
+
+#if HAS_SIGNAL != 0
 #include <signal.h>
 
 static void sighandler(int signum) {
@@ -75,7 +81,7 @@ static void sighandler(int signum) {
 void mp_hal_set_interrupt_char(char c) {
     // configure terminal settings to (not) let ctrl-C through
     if (c == CHAR_CTRL_C) {
-        #ifndef _WIN32
+        #if HAS_SIGNAL != 0
         // enable signal handler
         struct sigaction sa;
         sa.sa_flags = 0;
@@ -84,7 +90,7 @@ void mp_hal_set_interrupt_char(char c) {
         sigaction(SIGINT, &sa, NULL);
         #endif
     } else {
-        #ifndef _WIN32
+        #if HAS_SIGNAL != 0
         // disable signal handler
         struct sigaction sa;
         sa.sa_flags = 0;
diff --git a/ports/unix/variants/mpconfigvariant_common.h b/ports/unix/variants/mpconfigvariant_common.h
index 2e34055bf7..5f709d3b51 100644
--- a/ports/unix/variants/mpconfigvariant_common.h
+++ b/ports/unix/variants/mpconfigvariant_common.h
@@ -96,7 +96,9 @@
 #define MICROPY_PY_OS_ERRNO            (1)
 #define MICROPY_PY_OS_GETENV_PUTENV_UNSETENV (1)
 #define MICROPY_PY_OS_SEP              (1)
+#ifndef MICROPY_PY_OS_SYSTEM
 #define MICROPY_PY_OS_SYSTEM           (1)
+#endif
 #define MICROPY_PY_OS_URANDOM          (1)
 
 // Enable the unix-specific "time" module.
@@ -112,7 +114,9 @@
 #endif
 
 // The "select" module is enabled by default, but disable select.select().
+#ifndef MICROPY_PY_SELECT_POSIX_OPTIMISATIONS
 #define MICROPY_PY_SELECT_POSIX_OPTIMISATIONS (1)
+#endif
 #define MICROPY_PY_SELECT_SELECT       (0)
 
 // Enable the "websocket" module.
diff --git a/ports/unix/variants/wasi/manifest.py b/ports/unix/variants/wasi/manifest.py
new file mode 100644
index 0000000000..d27bf3c47f
--- /dev/null
+++ b/ports/unix/variants/wasi/manifest.py
@@ -0,0 +1,3 @@
+include("$(PORT_DIR)/variants/manifest.py")
+
+include("$(MPY_DIR)/extmod/asyncio")
diff --git a/ports/unix/variants/wasi/mpconfigvariant.h b/ports/unix/variants/wasi/mpconfigvariant.h
new file mode 100644
index 0000000000..95d0a47fe8
--- /dev/null
+++ b/ports/unix/variants/wasi/mpconfigvariant.h
@@ -0,0 +1,38 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Damien P. George
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+// Set base feature level.
+#define MICROPY_CONFIG_ROM_LEVEL (MICROPY_CONFIG_ROM_LEVEL_EXTRA_FEATURES)
+
+// WASI has different values for POLL constants.
+#define MICROPY_PY_SELECT_POSIX_OPTIMISATIONS (0)
+
+// WASI doesn't have executable or process.
+#define MICROPY_PY_OS_SYSTEM (0)
+#define MICROPY_PY_SYS_EXECUTABLE (0)
+
+// Enable extra Unix features.
+#include "../mpconfigvariant_common.h"
diff --git a/ports/unix/variants/wasi/mpconfigvariant.mk b/ports/unix/variants/wasi/mpconfigvariant.mk
new file mode 100644
index 0000000000..c78d9cc15b
--- /dev/null
+++ b/ports/unix/variants/wasi/mpconfigvariant.mk
@@ -0,0 +1,28 @@
+# Build for WASI
+
+FROZEN_MANIFEST ?= $(VARIANT_DIR)/manifest.py
+
+# WASI doesn't have FFI
+MICROPY_PY_FFI=0
+
+# When threading is enabled, micropython GC uses signals, which is
+# not available on WASI.
+MICROPY_PY_THREAD=0
+
+# Disable for now because network support is limited in WASI.
+MICROPY_PY_SOCKET=0
+MICROPY_PY_SSL=0
+
+# ../../lib/berkeley-db-1.xx/PORT/include/db.h:40:10:
+# fatal error: 'sys/cdefs.h' file not found
+MICROPY_PY_BTREE=0
+
+# WASI doesn't have termios
+MICROPY_PY_TERMIOS=0
+MICROPY_USE_READLINE=0
+
+# The following things might just work as they are.
+# Disabled for now because I'm not interested in them.
+MICROPY_VFS_FAT=0
+MICROPY_VFS_LFS1=0
+MICROPY_VFS_LFS2=0