diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2c34f334f..38bd9a2a7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -607,6 +607,8 @@ set(ZIG_STD_FILES
     "os/path.zig"
     "os/time.zig"
     "os/uefi.zig"
+    "os/wasi.zig"
+    "os/wasi/core.zig"
     "os/windows.zig"
     "os/windows/advapi32.zig"
     "os/windows/error.zig"
diff --git a/src/ir.cpp b/src/ir.cpp
index 3d4ab45dc..db45496f3 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -15828,6 +15828,13 @@ static void add_link_lib_symbol(IrAnalyze *ira, Buf *lib_name, Buf *symbol_name,
         ira->codegen->reported_bad_link_libc_error = true;
     }
 
+    bool is_wasi = buf_eql_str(lib_name, "wasi");
+    if (is_wasi && ira->codegen->zig_target->os != OsWASI) {
+        ir_add_error_node(ira, source_node,
+            buf_sprintf("linking against wasi library"));
+        ira->codegen->reported_bad_link_libc_error = true;
+    }
+
     LinkLib *link_lib = add_link_lib(ira->codegen, lib_name);
     for (size_t i = 0; i < link_lib->symbols.length; i += 1) {
         Buf *existing_symbol_name = link_lib->symbols.at(i);
@@ -15836,7 +15843,7 @@ static void add_link_lib_symbol(IrAnalyze *ira, Buf *lib_name, Buf *symbol_name,
         }
     }
 
-    if (!is_libc && !ira->codegen->have_pic && !ira->codegen->reported_bad_link_libc_error) {
+    if (!is_libc && !is_wasi && !ira->codegen->have_pic && !ira->codegen->reported_bad_link_libc_error) {
         ErrorMsg *msg = ir_add_error_node(ira, source_node,
             buf_sprintf("dependency on dynamic library '%s' requires enabling Position Independent Code",
                 buf_ptr(lib_name)));
diff --git a/src/link.cpp b/src/link.cpp
index 78e549c80..6c6ff07ba 100644
--- a/src/link.cpp
+++ b/src/link.cpp
@@ -1091,7 +1091,9 @@ static void construct_linker_job_wasm(LinkJob *lj) {
     CodeGen *g = lj->codegen;
 
     lj->args.append("-error-limit=0");
-    lj->args.append("--no-entry");  // So lld doesn't look for _start.
+    if (g->zig_target->os != OsWASI) {
+	    lj->args.append("--no-entry");  // So lld doesn't look for _start.
+    }
     lj->args.append("--allow-undefined");
     lj->args.append("--export-all");
     lj->args.append("-o");
diff --git a/std/os.zig b/std/os.zig
index d641cf29c..c1d5aa409 100644
--- a/std/os.zig
+++ b/std/os.zig
@@ -23,6 +23,7 @@ test "std.os" {
     _ = @import("os/time.zig");
     _ = @import("os/windows.zig");
     _ = @import("os/uefi.zig");
+    _ = @import("os/wasi.zig");
     _ = @import("os/get_app_data_dir.zig");
 }
 
@@ -33,6 +34,7 @@ pub const freebsd = @import("os/freebsd.zig");
 pub const netbsd = @import("os/netbsd.zig");
 pub const zen = @import("os/zen.zig");
 pub const uefi = @import("os/uefi.zig");
+pub const wasi = @import("os/wasi.zig");
 
 pub const posix = switch (builtin.os) {
     Os.linux => linux,
@@ -40,6 +42,7 @@ pub const posix = switch (builtin.os) {
     Os.freebsd => freebsd,
     Os.netbsd => netbsd,
     Os.zen => zen,
+    Os.wasi => wasi,
     else => @compileError("Unsupported OS"),
 };
 
@@ -187,7 +190,7 @@ pub fn abort() noreturn {
         c.abort();
     }
     switch (builtin.os) {
-        Os.linux, Os.macosx, Os.ios, Os.freebsd, Os.netbsd => {
+        Os.linux, Os.macosx, Os.ios, Os.freebsd, Os.netbsd, Os.wasi => {
             _ = posix.raise(posix.SIGABRT);
             _ = posix.raise(posix.SIGKILL);
             while (true) {}
diff --git a/std/os/wasi.zig b/std/os/wasi.zig
new file mode 100644
index 000000000..23c3a05af
--- /dev/null
+++ b/std/os/wasi.zig
@@ -0,0 +1,108 @@
+pub use @import("wasi/core.zig");
+
+// Based on https://github.com/CraneStation/wasi-sysroot/blob/wasi/libc-bottom-half/headers/public/wasi/core.h
+// and https://github.com/CraneStation/wasmtime/blob/master/docs/WASI-api.md
+
+pub const STDIN_FILENO = 0;
+pub const STDOUT_FILENO = 1;
+pub const STDERR_FILENO = 2;
+
+pub const ESUCCESS = 0;
+pub const E2BIG = 1;
+pub const EACCES = 2;
+pub const EADDRINUSE = 3;
+pub const EADDRNOTAVAIL = 4;
+pub const EAFNOSUPPORT = 5;
+pub const EAGAIN = 6;
+pub const EALREADY = 7;
+pub const EBADF = 8;
+pub const EBADMSG = 9;
+pub const EBUSY = 10;
+pub const ECANCELED = 11;
+pub const ECHILD = 12;
+pub const ECONNABORTED = 13;
+pub const ECONNREFUSED = 14;
+pub const ECONNRESET = 15;
+pub const EDEADLK = 16;
+pub const EDESTADDRREQ = 17;
+pub const EDOM = 18;
+pub const EDQUOT = 19;
+pub const EEXIST = 20;
+pub const EFAULT = 21;
+pub const EFBIG = 22;
+pub const EHOSTUNREACH = 23;
+pub const EIDRM = 24;
+pub const EILSEQ = 25;
+pub const EINPROGRESS = 26;
+pub const EINTR = 27;
+pub const EINVAL = 28;
+pub const EIO = 29;
+pub const EISCONN = 30;
+pub const EISDIR = 31;
+pub const ELOOP = 32;
+pub const EMFILE = 33;
+pub const EMLINK = 34;
+pub const EMSGSIZE = 35;
+pub const EMULTIHOP = 36;
+pub const ENAMETOOLONG = 37;
+pub const ENETDOWN = 38;
+pub const ENETRESET = 39;
+pub const ENETUNREACH = 40;
+pub const ENFILE = 41;
+pub const ENOBUFS = 42;
+pub const ENODEV = 43;
+pub const ENOENT = 44;
+pub const ENOEXEC = 45;
+pub const ENOLCK = 46;
+pub const ENOLINK = 47;
+pub const ENOMEM = 48;
+pub const ENOMSG = 49;
+pub const ENOPROTOOPT = 50;
+pub const ENOSPC = 51;
+pub const ENOSYS = 52;
+pub const ENOTCONN = 53;
+pub const ENOTDIR = 54;
+pub const ENOTEMPTY = 55;
+pub const ENOTRECOVERABLE = 56;
+pub const ENOTSOCK = 57;
+pub const ENOTSUP = 58;
+pub const ENOTTY = 59;
+pub const ENXIO = 60;
+pub const EOVERFLOW = 61;
+pub const EOWNERDEAD = 62;
+pub const EPERM = 63;
+pub const EPIPE = 64;
+pub const EPROTO = 65;
+pub const EPROTONOSUPPORT = 66;
+pub const EPROTOTYPE = 67;
+pub const ERANGE = 68;
+pub const EROFS = 69;
+pub const ESPIPE = 70;
+pub const ESRCH = 71;
+pub const ESTALE = 72;
+pub const ETIMEDOUT = 73;
+pub const ETXTBSY = 74;
+pub const EXDEV = 75;
+pub const ENOTCAPABLE = 76;
+
+// TODO: implement this like darwin does
+pub fn getErrno(r: usize) usize {
+    const signed_r = @bitCast(isize, r);
+    return if (signed_r > -4096 and signed_r < 0) @intCast(usize, -signed_r) else 0;
+}
+
+pub fn exit(status: i32) noreturn {
+    __wasi_proc_exit(@bitCast(__wasi_exitcode_t, isize(status)));
+}
+
+pub fn write(fd: i32, buf: [*]const u8, count: usize) usize {
+    var nwritten: usize = undefined;
+
+    const iovs = []__wasi_ciovec_t{__wasi_ciovec_t{
+        .buf = buf,
+        .buf_len = count,
+    }};
+
+    _ = __wasi_fd_write(@bitCast(__wasi_fd_t, isize(fd)), &iovs[0], iovs.len, &nwritten);
+    return nwritten;
+}
diff --git a/std/os/wasi/core.zig b/std/os/wasi/core.zig
new file mode 100644
index 000000000..cda06cdce
--- /dev/null
+++ b/std/os/wasi/core.zig
@@ -0,0 +1,17 @@
+pub const __wasi_errno_t = u16;
+pub const __wasi_exitcode_t = u32;
+pub const __wasi_fd_t = u32;
+pub const __wasi_signal_t = u8;
+
+pub const __wasi_ciovec_t = extern struct {
+    buf: [*]const u8,
+    buf_len: usize,
+};
+
+pub const __WASI_SIGABRT: __wasi_signal_t = 6;
+
+pub extern "wasi" fn __wasi_proc_raise(sig: __wasi_signal_t) __wasi_errno_t;
+
+pub extern "wasi" fn __wasi_proc_exit(rval: __wasi_exitcode_t) noreturn;
+
+pub extern "wasi" fn __wasi_fd_write(fd: __wasi_fd_t, iovs: *const __wasi_ciovec_t, iovs_len: usize, nwritten: *usize) __wasi_errno_t;
diff --git a/std/special/bootstrap.zig b/std/special/bootstrap.zig
index 32f913a5b..520561d54 100644
--- a/std/special/bootstrap.zig
+++ b/std/special/bootstrap.zig
@@ -20,6 +20,10 @@ comptime {
 }
 
 nakedcc fn _start() noreturn {
+    if (builtin.os == builtin.Os.wasi) {
+        std.os.wasi.__wasi_proc_exit(callMain());
+    }
+
     switch (builtin.arch) {
         builtin.Arch.x86_64 => {
             argc_ptr = asm ("lea (%%rsp), %[argc]"
diff --git a/std/special/panic.zig b/std/special/panic.zig
index 7cb714395..64d9bf39f 100644
--- a/std/special/panic.zig
+++ b/std/special/panic.zig
@@ -9,10 +9,15 @@ const std = @import("std");
 pub fn panic(msg: []const u8, error_return_trace: ?*builtin.StackTrace) noreturn {
     @setCold(true);
     switch (builtin.os) {
-        // TODO: fix panic in zen.
+        // TODO: fix panic in zen
         builtin.Os.freestanding, builtin.Os.zen => {
             while (true) {}
         },
+        builtin.Os.wasi => {
+            std.debug.warn("{}", msg);
+            _ = std.os.wasi.__wasi_proc_raise(std.os.wasi.__WASI_SIGABRT);
+            unreachable;
+        },
         builtin.Os.uefi => {
             // TODO look into using the debug info and logging helpful messages
             std.os.abort();