diff --git a/bin/mlton-script b/bin/mlton-script
index 296a2867a..ea8d8768a 100644
--- a/bin/mlton-script
+++ b/bin/mlton-script
@@ -118,6 +118,9 @@ for arg in "$@"; do
                -target-cc-opt ia64-hpux "-mlp64"                        \
                -target-cc-opt ia64 "-mtune=itanium2"                    \
                -target-cc-opt sparc '-m32 -mcpu=v8 -Wa,-xarch=v8plusa'  \
+               -target-cc-opt wasi '-D_WASI_EMULATED_SIGNAL'            \
+               -target-cc-opt wasi '-D_WASI_EMULATED_PROCESS_CLOCKS'    \
+               -target-cc-opt wasi '-D_WASI_EMULATED_GETPID'            \
                -target-cc-opt x86 '-m32'                                \
                -target-link-opt aix '-maix64'                           \
                -target-link-opt alpha                                   \
@@ -134,6 +137,9 @@ for arg in "$@"; do
                -target-link-opt mingw '-Wl,--enable-stdcall-fixup'      \
                -target-link-opt openbsd '-Wl,--no-execute-only'         \
                -target-link-opt solaris '-lnsl -lsocket -lrt'           \
+               -target-link-opt wasi '-lwasi-emulated-signal'           \
+               -target-link-opt wasi '-lwasi-emulated-process-clocks'   \
+               -target-link-opt wasi '-lwasi-emulated-getpid'           \
                -target-link-opt x86 '-m32'                              \
                -profile-exclude '\$\(SML_LIB\)'
     fi
diff --git a/runtime/Makefile b/runtime/Makefile
index ddbb740ff..89767521c 100644
--- a/runtime/Makefile
+++ b/runtime/Makefile
@@ -20,6 +20,8 @@ endif
 
 EXE :=
 
+WASMTIME :=
+
 MDVARIANTS := OPT DBG
 PIVARIANTS := DPI NPI PIC PIE
 
@@ -110,6 +112,16 @@ ifeq ($(TARGET_OS), cygwin)
 EXE := .exe
 endif
 
+ifeq ($(TARGET_OS), wasi)
+WASMTIME := wasmtime
+XCPPFLAGS += -D_WASI_EMULATED_SIGNAL \
+             -D_WASI_EMULATED_PROCESS_CLOCKS \
+             -D_WASI_EMULATED_GETPID
+XLDFLAGS += -lwasi-emulated-signal \
+            -lwasi-emulated-process-clocks \
+            -lwasi-emulated-getpid
+endif
+
 ifeq ($(TARGET_OS), mingw)
 EXE := .exe
 # GCC doesn't recognize the %I64 format specifier which means %ll on windows
@@ -239,11 +251,11 @@ ml-types.h: gen/ml-types.h
 	$(CP) $< $@
 
 gen/ml-types.h: gen/gen-types$(EXE)
-	./gen/gen-types$(EXE) ml-types.h > gen/ml-types.h
+	$(WASMTIME) ./gen/gen-types$(EXE) ml-types.h > gen/ml-types.h
 gen/c-types.h: gen/gen-types$(EXE)
-	./gen/gen-types$(EXE) c-types.h > gen/c-types.h
+	$(WASMTIME) ./gen/gen-types$(EXE) c-types.h > gen/c-types.h
 gen/c-types.sml: gen/gen-types$(EXE)
-	./gen/gen-types$(EXE) c-types.sml > gen/c-types.sml
+	$(WASMTIME) ./gen/gen-types$(EXE) c-types.sml > gen/c-types.sml
 
 ifneq ($(MAKECMDGOALS),clean)
 -include gen/gen-types.d
@@ -262,7 +274,7 @@ gen/$(1): gen/gen-basis-ffi.sml gen/basis-ffi.def
 	touch gen/$(1)
 else
 gen/$(1): gen/gen-basis-ffi$(EXE) gen/basis-ffi.def
-	./gen/gen-basis-ffi$(EXE) $(1) < gen/basis-ffi.def > gen/$(1)
+	$(WASMTIME) ./gen/gen-basis-ffi$(EXE) $(1) < gen/basis-ffi.def > gen/$(1)
 	$(CAT) gen/gen-basis-ffi.sml gen/basis-ffi.def gen/$(1) | $(SHA1DGST) > gen/$(1).chk
 endif
 endef
@@ -307,7 +319,7 @@ gdtoa/README: gdtoa.tgz gdtoa.may_alias-unions.patch gdtoa.rename-public-fns.pat
 	@touch $@
 
 gdtoa/arith.h: gdtoa/arithchk$(EXE)
-	./gdtoa/arithchk$(EXE) > gdtoa/arith.h
+	$(WASMTIME) ./gdtoa/arithchk$(EXE) > gdtoa/arith.h
 
 gdtoa/arithchk.c: gdtoa/README
 	@touch $@
@@ -319,7 +331,7 @@ ifneq ($(MAKECMDGOALS),clean)
 endif
 
 gdtoa/gd_qnan.h: gdtoa/qnan$(EXE)
-	./gdtoa/qnan$(EXE) > gdtoa/gd_qnan.h
+	$(WASMTIME) ./gdtoa/qnan$(EXE) > gdtoa/gd_qnan.h
 
 gdtoa/qnan.c: gdtoa/README
 	@touch $@
@@ -348,7 +360,7 @@ $(eval $(call A_TEMPLATE,mlton,MLTON))
 ### gen/constants ###
 
 gen/constants: gen/gen-constants$(EXE)
-	./gen/gen-constants > gen/constants
+	$(WASMTIME) ./gen/gen-constants > gen/constants
 
 ifneq ($(MAKECMDGOALS),clean)
 -include gen/gen-constants.d
diff --git a/runtime/cenv.h b/runtime/cenv.h
index e21503517..7e40347df 100644
--- a/runtime/cenv.h
+++ b/runtime/cenv.h
@@ -82,6 +82,8 @@ COMPILE_TIME_ASSERT(sizeof_double__is_eight, sizeof(double) == 8);
 #include "platform/openbsd.h"
 #elif (defined (__sun__))
 #include "platform/solaris.h"
+#elif (defined (__wasi__))
+#include "platform/wasi.h"
 #else
 #error unknown platform os
 #endif
@@ -117,6 +119,8 @@ COMPILE_TIME_ASSERT(sizeof_double__is_eight, sizeof(double) == 8);
 #include "platform/x86.h"
 #elif (defined (__loongarch64))
 #include "platform/loongarch64.h"
+#elif (defined (__wasm32))
+#include "platform/wasm32.h"
 #else
 #error unknown platform arch
 #endif
diff --git a/runtime/gc/heap.c b/runtime/gc/heap.c
index af1d9f8bb..668315d51 100644
--- a/runtime/gc/heap.c
+++ b/runtime/gc/heap.c
@@ -183,7 +183,9 @@ void shrinkHeap (GC_state s, GC_heap h, size_t keepSize) {
     }
     assert (isAligned (keepWithMapsSize, s->sysvals.pageSize));
     assert (keepWithMapsSize <= h->withMapsSize);
+#if HAS_SHRINK_HEAP
     GC_release (h->start + keepWithMapsSize, h->withMapsSize - keepWithMapsSize);
+#endif
     h->size = keepSize;
     h->withMapsSize = keepWithMapsSize;
   }
diff --git a/runtime/platform.h b/runtime/platform.h
index 6c3a44cfd..c88ea3b85 100644
--- a/runtime/platform.h
+++ b/runtime/platform.h
@@ -35,6 +35,10 @@
 #error HAS_REMAP not defined
 #endif
 
+#ifndef HAS_SHRINK_HEAP
+#error HAS_SHRINK_HEAP not defined
+#endif
+
 #ifndef HAS_SIGALTSTACK
 #error HAS_SIGALTSTACK not defined
 #else
diff --git a/runtime/platform/aix.h b/runtime/platform/aix.h
index 4869551f3..f7bb19037 100644
--- a/runtime/platform/aix.h
+++ b/runtime/platform/aix.h
@@ -34,6 +34,7 @@
 #define HAS_MSG_DONTWAIT FALSE
 #define HAS_PTRACE FALSE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/cygwin.h b/runtime/platform/cygwin.h
index 644fec5aa..29a0e7bae 100644
--- a/runtime/platform/cygwin.h
+++ b/runtime/platform/cygwin.h
@@ -35,6 +35,7 @@
 
 #define HAS_FEROUND FALSE
 #define HAS_REMAP TRUE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK FALSE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN TRUE
diff --git a/runtime/platform/darwin.h b/runtime/platform/darwin.h
index e5af03e32..ac2a0d936 100644
--- a/runtime/platform/darwin.h
+++ b/runtime/platform/darwin.h
@@ -34,6 +34,7 @@
 #define HAS_FEROUND TRUE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/freebsd.h b/runtime/platform/freebsd.h
index 85d685df0..919127ec1 100644
--- a/runtime/platform/freebsd.h
+++ b/runtime/platform/freebsd.h
@@ -30,6 +30,7 @@
 #define HAS_FEROUND TRUE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/hpux.h b/runtime/platform/hpux.h
index 62d83b649..aa8de42de 100644
--- a/runtime/platform/hpux.h
+++ b/runtime/platform/hpux.h
@@ -52,6 +52,7 @@
 #define HAS_FEROUND TRUE
 #define HAS_MSG_DONTWAIT FALSE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/hurd.h b/runtime/platform/hurd.h
index 7dbc46d5c..68fc44e88 100644
--- a/runtime/platform/hurd.h
+++ b/runtime/platform/hurd.h
@@ -30,6 +30,7 @@
 #define HAS_FEROUND TRUE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP TRUE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/linux.h b/runtime/platform/linux.h
index 3f1ce7a60..423f9e11b 100644
--- a/runtime/platform/linux.h
+++ b/runtime/platform/linux.h
@@ -38,6 +38,7 @@
 #endif
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP TRUE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #if (defined (__hppa__))
 #define NEEDS_SIGALTSTACK_EXEC TRUE
diff --git a/runtime/platform/mingw.h b/runtime/platform/mingw.h
index f99352eb0..7441ee5e2 100644
--- a/runtime/platform/mingw.h
+++ b/runtime/platform/mingw.h
@@ -33,6 +33,7 @@
 #define HAS_FEROUND FALSE
 #define HAS_MSG_DONTWAIT FALSE
 #define HAS_REMAP TRUE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK FALSE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN TRUE
diff --git a/runtime/platform/netbsd.h b/runtime/platform/netbsd.h
index d2aef2e84..6bea1a501 100644
--- a/runtime/platform/netbsd.h
+++ b/runtime/platform/netbsd.h
@@ -30,6 +30,7 @@
 #define HAS_FEROUND FALSE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/openbsd.h b/runtime/platform/openbsd.h
index c6ca591e6..ffb816e0c 100644
--- a/runtime/platform/openbsd.h
+++ b/runtime/platform/openbsd.h
@@ -30,6 +30,7 @@
 #define HAS_FEROUND FALSE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/solaris.h b/runtime/platform/solaris.h
index 456d7fc7e..b752f3454 100644
--- a/runtime/platform/solaris.h
+++ b/runtime/platform/solaris.h
@@ -34,6 +34,7 @@
 #define HAS_FEROUND TRUE
 #define HAS_MSG_DONTWAIT TRUE
 #define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP TRUE
 #define HAS_SIGALTSTACK TRUE
 #define NEEDS_SIGALTSTACK_EXEC FALSE
 #define HAS_SPAWN FALSE
diff --git a/runtime/platform/wasi.c b/runtime/platform/wasi.c
new file mode 100644
index 000000000..42dc82b44
--- /dev/null
+++ b/runtime/platform/wasi.c
@@ -0,0 +1,71 @@
+#include "platform.h"
+
+/* WASI only implements a subset of POSIX, and given how it works it doesn't
+ * make too much sense to try too hard to emulate missing functionality.
+ *
+ * Every function needed by the runtime library and not provided by WASI
+ * is declared in wasi.h, but only a tiny number are implemented here.
+ *
+ * This means that any use of missing runtime functions from SML code will
+ * result in linker errors at the end of compilation, rather than as a runtime
+ * error later.
+ *
+ * The functions in this file are the bare minimum to get the GC working,
+ * needed by every program compiled by MLton.
+ */
+
+size_t GC_pageSize (void) {
+        return PAGESIZE;
+}
+
+uintmax_t GC_physMem (void) {
+        /* WASI doesn't provide a way to query actual physical memory, so pick
+         * a reasonable amount (as of Feb 2024).
+         */
+        return 1 << 30;  /* 1 GiB */
+}
+
+void *GC_mmapAnon (__attribute__ ((unused)) void *start, size_t length) {
+        void *mem;
+        int err = posix_memalign (&mem, PAGESIZE, length);
+        if (err) {
+                return (void *) -1;
+        }
+        return memset (mem, 0, length);
+}
+
+void *GC_mmapAnonFlags (void *start, size_t length,
+                        __attribute__ ((unused)) int flags) {
+        return GC_mmapAnon (start, length);
+}
+
+void GC_release (void *base, __attribute__ ((unused)) size_t length) {
+        free (base);
+}
+
+void GC_displayMem (void) {
+        size_t memory_size = (size_t) sbrk(0);
+        size_t pages = memory_size / PAGESIZE;
+        printf ("memory.size: pages=%zu, pagesize=%d, total=%zu\n",
+                pages, PAGESIZE, memory_size);
+}
+
+void GC_diskBack_close (__attribute__ ((unused)) void *data) {
+        die ("Disk-backed heap not supported on WASI");
+}
+
+void GC_diskBack_read (__attribute__ ((unused)) void *data,
+                       __attribute__ ((unused)) pointer buf,
+                       __attribute__ ((unused)) size_t size) {
+        die ("Disk-backed heap not supported on WASI");
+}
+
+void *GC_diskBack_write (__attribute__ ((unused)) pointer buf,
+                         __attribute__ ((unused)) size_t size) {
+        die ("Disk-backed heap not supported on WASI");
+}
+
+int sigemptyset (sigset_t *set) {
+        *set = (sigset_t) 0;
+        return 0;
+}
diff --git a/runtime/platform/wasi.h b/runtime/platform/wasi.h
new file mode 100644
index 000000000..e978246bf
--- /dev/null
+++ b/runtime/platform/wasi.h
@@ -0,0 +1,490 @@
+#define _GNU_SOURCE
+
+#include <dirent.h>
+#include <fcntl.h>
+#include <fenv.h>
+#include <inttypes.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
+#include <poll.h>
+#include <sys/ioctl.h>
+#include <sys/resource.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/sysinfo.h>
+#include <sys/time.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <utime.h>
+
+#define HAS_FEROUND TRUE
+#define HAS_MSG_DONTWAIT TRUE
+#define HAS_REMAP FALSE
+#define HAS_SHRINK_HEAP FALSE
+#define HAS_SIGALTSTACK FALSE
+#define NEEDS_SIGALTSTACK_EXEC FALSE
+#define HAS_SPAWN FALSE
+#define HAS_TIME_PROFILING FALSE
+
+#define MLton_Platform_OS_host "wasi"
+
+/*
+ * The definitions below are missing from WASI but are required by the runtime.
+ *
+ * In a small number of cases, these are implemented in wasi.c, but most of them
+ * are not. See wasi.c for a discussion.
+ *
+ * These are not guarded by ifdefs so that we can easily detect when functionality
+ * is added to WASI.
+ *
+ * This file is roughly based on the mingw implementation.
+ */
+
+/* ------------------------------------------------- */
+/*                      Itimer                       */
+/* ------------------------------------------------- */
+
+#define ITIMER_REAL    0
+#define ITIMER_VIRTUAL 1
+#define ITIMER_PROF    2
+
+struct itimerval {
+        struct timeval it_interval;
+        struct timeval it_value;
+};
+
+int setitimer (int, const struct itimerval *, struct itimerval *);
+
+/* ------------------------------------------------- */
+/*                        Rlimit                     */
+/* ------------------------------------------------- */
+
+#define RLIMIT_CPU      0
+#define RLIMIT_FSIZE    1
+#define RLIMIT_DATA     2
+#define RLIMIT_STACK    3
+#define RLIMIT_CORE     4
+#define RLIMIT_NOFILE   5
+#define RLIMIT_AS       6
+#define RLIMIT_NLIMITS  7
+
+#define RLIM_INFINITY   (0xffffffffUL)
+
+typedef unsigned long rlim_t;
+
+struct rlimit {
+        rlim_t  rlim_cur;
+        rlim_t  rlim_max;
+};
+
+int getrlimit (int resource, struct rlimit *);
+int setrlimit (int resource, const struct rlimit *);
+
+/* ------------------------------------------------- */
+/*                    Networking                     */
+/* ------------------------------------------------- */
+
+struct servent {
+        char *s_name;
+        char **s_aliases;
+        int s_port;
+        char *s_proto;
+};
+
+struct servent *getservbyname (const char *, const char *);
+extern struct servent *getservbyport (int, const char *);
+
+struct hostent {
+        char *h_name;
+        char **h_aliases;
+        int h_addrtype;
+        int h_length;
+        char **h_addr_list;
+};
+
+struct hostent *gethostbyaddr (const void *, socklen_t, int);
+struct hostent *gethostbyname (const char *);
+
+int socket (int, int, int);
+int socketpair (int, int, int, int [2]);
+int bind (int, const struct sockaddr *, socklen_t);
+int connect (int, const struct sockaddr *, socklen_t);
+int listen (int, int);
+ssize_t recvfrom (int, void *, size_t, int, struct sockaddr *, socklen_t *);
+ssize_t sendto (int, const void *, size_t, int, const struct sockaddr *, socklen_t);
+int setsockopt (int, int, int, const void *, socklen_t);
+int getpeername (int, struct sockaddr *, socklen_t *);
+int gethostname(char *, size_t);
+int getsockname (int, struct sockaddr *, socklen_t *);
+
+#define SIOCATMARK      0x8905
+
+#define SO_DEBUG        1
+#define SO_REUSEADDR    2
+#define SO_TYPE         3
+#define SO_ERROR        4
+#define SO_DONTROUTE    5
+#define SO_BROADCAST    6
+#define SO_SNDBUF       7
+#define SO_RCVBUF       8
+#define SO_KEEPALIVE    9
+#define SO_OOBINLINE    10
+#define SO_NO_CHECK     11
+#define SO_PRIORITY     12
+#define SO_LINGER       13
+#define SO_BSDCOMPAT    14
+#define SO_REUSEPORT    15
+#define SO_PASSCRED     16
+#define SO_PEERCRED     17
+#define SO_RCVLOWAT     18
+#define SO_SNDLOWAT     19
+#define SO_ACCEPTCONN   30
+#define SO_PEERSEC      31
+#define SO_SNDBUFFORCE  32
+#define SO_RCVBUFFORCE  33
+#define SO_PROTOCOL     38
+#define SO_DOMAIN       39
+#define SO_RCVTIMEO     66
+#define SO_SNDTIMEO     67
+
+#define SOCK_RAW       3
+#define SOCK_RDM       4
+#define SOCK_SEQPACKET 5
+#define SOCK_DCCP      6
+#define SOCK_PACKET    10
+
+struct sockaddr_un {
+        sa_family_t sun_family;
+        char sun_path[108];
+};
+
+#define MSG_OOB       0x0001
+#define MSG_DONTROUTE 0x0004
+#define MSG_CTRUNC    0x0008
+#define MSG_PROXY     0x0010
+#define MSG_DONTWAIT  0x0040
+#define MSG_EOR       0x0080
+
+struct protoent {
+  char *p_name;
+  char **p_aliases;
+  int p_proto;
+};
+
+struct protoent *getprotobyname (const char *);
+struct protoent *getprotobynumber (int);
+
+/* ------------------------------------------------- */
+/*                       Files                       */
+/* ------------------------------------------------- */
+
+#define F_DUPFD  0
+#define F_GETOWN 5
+#define F_SETOWN 6
+#define F_GETLK  7
+#define F_SETLK  8
+
+#define F_RDLCK 1
+#define F_WRLCK 2
+#define F_UNLCK 3
+
+#define F_SETLKW 9
+
+int chmod(const char *, mode_t);
+int chown (const char *, uid_t, gid_t);
+int fchdir (int);
+int fchmod (int, mode_t);
+int fchown (int, uid_t, gid_t);
+long fpathconf (int, int);
+int link (const char *, const char *);
+int lstat (const char *, struct stat *);
+int mkfifo (const char *, mode_t);
+int mkstemp (char *);
+long pathconf (const char *, int);
+int symlink (const char *, const char *);
+int truncate (const char *, off_t);
+mode_t umask(mode_t);
+
+int dup(int);
+int dup2(int, int);
+int fcntl (int, int, ...);
+int fsync (int);
+int pipe (int [2]);
+
+/* ------------------------------------------------- */
+/*                    Processes                      */
+/* ------------------------------------------------- */
+
+struct tms {
+        int tms_utime;
+        int tms_stime;
+        int tms_cutime;
+        int tms_cstime;
+};
+
+struct utsname {
+        char machine[20];
+        char nodename[256];
+        char release[20];
+        char sysname[30];
+        char version[20];
+};
+
+char *getlogin (void);
+char *ctermid (char *);
+gid_t getegid (void);
+uid_t geteuid (void);
+gid_t getgid (void);
+int getgroups (int, gid_t []);
+pid_t getpgid(pid_t);
+pid_t getpgrp(void);
+pid_t getppid (void);
+uid_t getuid (void);
+int setenv (const char *, const char *, int);
+int setgid (gid_t);
+int setgroups (size_t, const gid_t *);
+int setpgid (pid_t, pid_t);
+pid_t setsid (void);
+int setuid (uid_t);
+clock_t times (struct tms *);
+char *ttyname (int);
+int uname (struct utsname *);
+
+#define POLLPRI 0x002
+
+#define WNOHANG   1
+#define WUNTRACED 2
+
+#define WIFEXITED(w)    ((w) & 0)
+#define WIFSIGNALED(w)  ((w) & 0)
+#define WIFSTOPPED(w)   ((w) & 0)
+#define WTERMSIG(w)     ((w) & 0)
+#define WEXITSTATUS(w)  ((w) & 0)
+#define WSTOPSIG        WEXITSTATUS
+
+int alarm(int);
+int execve(const char *, char *const [], char *const []);
+int execvp(const char *, char *const []);
+pid_t fork(void);
+int kill(pid_t, int);
+int pause(void);
+pid_t waitpid (pid_t, int *, int);
+
+/* ------------------------------------------------- */
+/*                      Signals                      */
+/* ------------------------------------------------- */
+
+#define SIG_BLOCK     0
+#define SIG_UNBLOCK   1
+#define SIG_SETMASK   2
+
+struct sigaction {
+        int             sa_flags;
+        sigset_t        sa_mask;
+        void (*sa_handler)(int);
+};
+
+int sigaction (int, const struct sigaction *, struct sigaction *);
+int sigaddset (sigset_t *, int);
+int sigdelset (sigset_t *, int);
+int sigemptyset (sigset_t *);
+int sigfillset (sigset_t *);
+int sigismember (const sigset_t *, int);
+int sigpending (sigset_t *);
+int sigprocmask (int, const sigset_t *, sigset_t *);
+int sigsuspend (const sigset_t *);
+
+/* ------------------------------------------------- */
+/*                       Passwd                      */
+/* ------------------------------------------------- */
+
+struct group {
+        gid_t   gr_gid;
+        char    **gr_mem;
+        char    *gr_name;
+        char    *gr_passwd;
+};
+
+struct passwd {
+        char    *pw_dir;
+        gid_t   pw_gid;
+        char    *pw_name;
+        char    *pw_shell;
+        uid_t   pw_uid;
+};
+
+struct group *getgrgid (gid_t);
+struct group *getgrnam (const char *);
+struct passwd *getpwnam (const char *);
+struct passwd *getpwuid (uid_t);
+
+/* ------------------------------------------------- */
+/*                        TTY                        */
+/* ------------------------------------------------- */
+
+#define B0       0x00000
+#define B50      0x00001
+#define B75      0x00002
+#define B110     0x00003
+#define B134     0x00004
+#define B150     0x00005
+#define B200     0x00006
+#define B300     0x00007
+#define B600     0x00008
+#define B1200    0x00009
+#define B1800    0x0000a
+#define B2400    0x0000b
+#define B4800    0x0000c
+#define B9600    0x0000d
+#define B19200   0x0000e
+#define B38400   0x0000f
+
+#define VEOL            2
+#define VEOL2           3
+#define VEOF            4
+#define VERASE          5
+#define VINTR           6
+#define VKILL           7
+#define VLNEXT          8
+#define VMIN            9
+#define VQUIT           10
+#define VREPRINT        11
+#define VSTART          12
+#define VSTOP           13
+#define VSUSP           14
+#define VSWTC           15
+#define VTIME           16
+#define VWERASE         17
+#define NCCS            18
+
+#define IGNBRK  0x00001
+#define BRKINT  0x00002
+#define IGNPAR  0x00004
+#define IMAXBEL 0x00008
+#define INPCK   0x00010
+#define ISTRIP  0x00020
+#define INLCR   0x00040
+#define IGNCR   0x00080
+#define ICRNL   0x00100
+#define IXON    0x00400
+#define IXOFF   0x01000
+#define IUCLC   0x04000
+#define IXANY   0x08000
+#define PARMRK  0x10000
+#define OPOST   0x00001
+
+#define CSIZE    0x00030
+#define CS5      0x00000
+#define CS6      0x00010
+#define CS7      0x00020
+#define CS8      0x00030
+#define CSTOPB   0x00040
+#define CREAD    0x00080
+#define PARENB   0x00100
+#define PARODD   0x00200
+#define HUPCL    0x00400
+#define CLOCAL   0x00800
+#define CBAUDEX  0x0100f
+#define B57600   0x01001
+#define B115200  0x01002
+#define B128000  0x01003
+#define B230400  0x01004
+#define B256000  0x01005
+#define CRTSXOFF 0x04000
+#define CRTSCTS  0x08000
+
+#define ISIG    0x0001
+#define ICANON  0x0002
+#define ECHO    0x0004
+#define ECHOE   0x0008
+#define ECHOK   0x0010
+#define ECHONL  0x0020
+#define NOFLSH  0x0040
+#define TOSTOP  0x0080
+#define IEXTEN  0x0100
+#define FLUSHO  0x0200
+#define ECHOKE  0x0400
+#define ECHOCTL 0x0800
+
+#define TCOOFF          0
+#define TCOON           1
+#define TCIOFF          2
+#define TCION           3
+
+#define TCIFLUSH        0
+#define TCOFLUSH        1
+#define TCIOFLUSH       2
+#define TCFLSH          3
+
+#define TCSAFLUSH       1
+#define TCSANOW         2
+#define TCSADRAIN       3
+#define TCSADFLUSH      4
+
+typedef unsigned char cc_t;
+typedef unsigned int speed_t;
+typedef unsigned int tcflag_t;
+
+struct termios {
+        cc_t c_cc[NCCS];
+        tcflag_t c_cflag;
+        tcflag_t c_iflag;
+        tcflag_t c_lflag;
+        tcflag_t c_oflag;
+};
+
+speed_t cfgetispeed (struct termios *);
+speed_t cfgetospeed (struct termios *);
+int cfsetispeed (struct termios *, speed_t);
+int cfsetospeed (struct termios *, speed_t);
+int tcdrain (int);
+int tcflow (int, int);
+int tcflush (int, int);
+int tcgetattr (int, struct termios *);
+pid_t tcgetpgrp (int);
+int tcsendbreak (int, int);
+int tcsetattr (int, int, struct termios *);
+int tcsetpgrp (int, pid_t);
+
+/* ------------------------------------------------- */
+/*                      Syslog                       */
+/* ------------------------------------------------- */
+
+#define LOG_DEBUG   0
+#define LOG_INFO    1
+#define LOG_NOTICE  2
+#define LOG_WARNING 3
+#define LOG_ERR     4
+#define LOG_CRIT    5
+#define LOG_ALERT   6
+#define LOG_EMERG   7
+
+#define LOG_PID    0x01
+#define LOG_CONS   0x02
+#define LOG_ODELAY 0x04
+#define LOG_NDELAY 0x08
+#define LOG_NOWAIT 0x10
+#define LOG_PERROR 0x20
+
+#define LOG_AUTH   1
+#define LOG_CRON   2
+#define LOG_DAEMON 3
+#define LOG_KERN   4
+#define LOG_LOCAL0 5
+#define LOG_LOCAL1 6
+#define LOG_LOCAL2 7
+#define LOG_LOCAL3 8
+#define LOG_LOCAL4 9
+#define LOG_LOCAL5 10
+#define LOG_LOCAL6 11
+#define LOG_LOCAL7 12
+#define LOG_LPR    13
+#define LOG_MAIL   14
+#define LOG_NEWS   15
+#define LOG_SYSLOG 16
+#define LOG_USER   17
+#define LOG_UUCP   18
+
+void openlog (const char *, int, int);
+void closelog (void);
+void syslog (int, const char *, const char *);
diff --git a/runtime/platform/wasm32.h b/runtime/platform/wasm32.h
new file mode 100644
index 000000000..28575ef4b
--- /dev/null
+++ b/runtime/platform/wasm32.h
@@ -0,0 +1 @@
+#define MLton_Platform_Arch_host "wasm32"