diff --git a/lib/std/c/wasi.zig b/lib/std/c/wasi.zig
index c7533dce92..56f1e77805 100644
--- a/lib/std/c/wasi.zig
+++ b/lib/std/c/wasi.zig
@@ -40,12 +40,6 @@ pub const E = wasi.errno_t;
 
 pub const CLOCK = wasi.clockid_t;
 pub const IOV_MAX = 1024;
-pub const LOCK = struct {
-    pub const SH = 0x1;
-    pub const EX = 0x2;
-    pub const NB = 0x4;
-    pub const UN = 0x8;
-};
 pub const S = struct {
     pub const IEXEC = @compileError("TODO audit this");
     pub const IFBLK = 0x6000;
diff --git a/lib/std/fs/Dir.zig b/lib/std/fs/Dir.zig
index b6222f942f..89b1d18b9c 100644
--- a/lib/std/fs/Dir.zig
+++ b/lib/std/fs/Dir.zig
@@ -800,7 +800,7 @@ pub fn openFile(self: Dir, sub_path: []const u8, flags: File.OpenFlags) File.Ope
         const path_w = try windows.sliceToPrefixedFileW(self.fd, sub_path);
         return self.openFileW(path_w.span(), flags);
     }
-    if (native_os == .wasi) {
+    if (native_os == .wasi and !builtin.link_libc) {
         var base: std.os.wasi.rights_t = .{};
         if (flags.isRead()) {
             base.FD_READ = true;
@@ -834,17 +834,25 @@ pub fn openFileZ(self: Dir, sub_path: [*:0]const u8, flags: File.OpenFlags) File
             const path_w = try windows.cStrToPrefixedFileW(self.fd, sub_path);
             return self.openFileW(path_w.span(), flags);
         },
-        .wasi => {
+        // Use the libc API when libc is linked because it implements things
+        // such as opening absolute file paths.
+        .wasi => if (!builtin.link_libc) {
             return openFile(self, mem.sliceTo(sub_path, 0), flags);
         },
         else => {},
     }
 
-    var os_flags: posix.O = .{
-        .ACCMODE = switch (flags.mode) {
-            .read_only => .RDONLY,
-            .write_only => .WRONLY,
-            .read_write => .RDWR,
+    var os_flags: posix.O = switch (native_os) {
+        .wasi => .{
+            .read = flags.mode != .write_only,
+            .write = flags.mode != .read_only,
+        },
+        else => .{
+            .ACCMODE = switch (flags.mode) {
+                .read_only => .RDONLY,
+                .write_only => .WRONLY,
+                .read_write => .RDWR,
+            },
         },
     };
     if (@hasField(posix.O, "CLOEXEC")) os_flags.CLOEXEC = true;
diff --git a/lib/std/posix.zig b/lib/std/posix.zig
index e80e64b45e..857c8dd1e2 100644
--- a/lib/std/posix.zig
+++ b/lib/std/posix.zig
@@ -1602,6 +1602,10 @@ pub fn openZ(file_path: [*:0]const u8, flags: O, perm: mode_t) OpenError!fd_t {
             .PERM => return error.AccessDenied,
             .EXIST => return error.PathAlreadyExists,
             .BUSY => return error.DeviceBusy,
+            .ILSEQ => |err| if (native_os == .wasi)
+                return error.InvalidUtf8
+            else
+                return unexpectedErrno(err),
             else => |err| return unexpectedErrno(err),
         }
     }
@@ -1771,6 +1775,10 @@ pub fn openatZ(dir_fd: fd_t, file_path: [*:0]const u8, flags: O, mode: mode_t) O
             .OPNOTSUPP => return error.FileLocksNotSupported,
             .AGAIN => return error.WouldBlock,
             .TXTBSY => return error.FileBusy,
+            .ILSEQ => |err| if (native_os == .wasi)
+                return error.InvalidUtf8
+            else
+                return unexpectedErrno(err),
             else => |err| return unexpectedErrno(err),
         }
     }