diff --git a/lib/std/Thread.zig b/lib/std/Thread.zig
index c12679233660..adb822173e43 100644
--- a/lib/std/Thread.zig
+++ b/lib/std/Thread.zig
@@ -75,7 +75,7 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
                 }
             } else {
                 const err = std.c.pthread_setname_np(self.getHandle(), name_with_terminator.ptr);
-                switch (err) {
+                switch (@as(posix.E, @enumFromInt(err))) {
                     .SUCCESS => return,
                     .RANGE => unreachable,
                     else => |e| return posix.unexpectedErrno(e),
@@ -119,14 +119,14 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
             if (self.getHandle() != std.c.pthread_self()) return error.Unsupported;
 
             const err = std.c.pthread_setname_np(name_with_terminator.ptr);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return,
                 else => |e| return posix.unexpectedErrno(e),
             }
         },
         .netbsd, .solaris, .illumos => if (use_pthreads) {
             const err = std.c.pthread_setname_np(self.getHandle(), name_with_terminator.ptr, null);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return,
                 .INVAL => unreachable,
                 .SRCH => unreachable,
@@ -144,7 +144,7 @@ pub fn setName(self: Thread, name: []const u8) SetNameError!void {
         },
         .dragonfly => if (use_pthreads) {
             const err = std.c.pthread_setname_np(self.getHandle(), name_with_terminator.ptr);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return,
                 .INVAL => unreachable,
                 .FAULT => unreachable,
@@ -180,7 +180,7 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
                 }
             } else {
                 const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-                switch (err) {
+                switch (@as(posix.E, @enumFromInt(err))) {
                     .SUCCESS => return std.mem.sliceTo(buffer, 0),
                     .RANGE => unreachable,
                     else => |e| return posix.unexpectedErrno(e),
@@ -219,7 +219,7 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
         },
         .macos, .ios, .watchos, .tvos, .visionos => if (use_pthreads) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return std.mem.sliceTo(buffer, 0),
                 .SRCH => unreachable,
                 else => |e| return posix.unexpectedErrno(e),
@@ -227,7 +227,7 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
         },
         .netbsd, .solaris, .illumos => if (use_pthreads) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return std.mem.sliceTo(buffer, 0),
                 .INVAL => unreachable,
                 .SRCH => unreachable,
@@ -243,7 +243,7 @@ pub fn getName(self: Thread, buffer_ptr: *[max_name_len:0]u8) GetNameError!?[]co
         },
         .dragonfly => if (use_pthreads) {
             const err = std.c.pthread_getname_np(self.getHandle(), buffer.ptr, max_name_len + 1);
-            switch (err) {
+            switch (@as(posix.E, @enumFromInt(err))) {
                 .SUCCESS => return std.mem.sliceTo(buffer, 0),
                 .INVAL => unreachable,
                 .FAULT => unreachable,
diff --git a/lib/std/c/darwin.zig b/lib/std/c/darwin.zig
index dfc0fd56ea00..ac2af38c1c02 100644
--- a/lib/std/c/darwin.zig
+++ b/lib/std/c/darwin.zig
@@ -851,8 +851,8 @@ pub const pthread_attr_t = extern struct {
 };
 
 pub extern "c" fn pthread_threadid_np(thread: ?std.c.pthread_t, thread_id: *u64) c_int;
-pub extern "c" fn pthread_setname_np(name: [*:0]const u8) E;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
+pub extern "c" fn pthread_setname_np(name: [*:0]const u8) c_int;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
 pub extern "c" fn pthread_attr_set_qos_class_np(attr: *pthread_attr_t, qos_class: qos_class_t, relative_priority: c_int) c_int;
 pub extern "c" fn pthread_attr_get_qos_class_np(attr: *pthread_attr_t, qos_class: *qos_class_t, relative_priority: *c_int) c_int;
 pub extern "c" fn pthread_set_qos_class_self_np(qos_class: qos_class_t, relative_priority: c_int) c_int;
diff --git a/lib/std/c/dragonfly.zig b/lib/std/c/dragonfly.zig
index cc72aaa072eb..8903b6abd268 100644
--- a/lib/std/c/dragonfly.zig
+++ b/lib/std/c/dragonfly.zig
@@ -29,8 +29,8 @@ pub const pthread_attr_t = extern struct { // copied from freebsd
 
 pub const sem_t = ?*opaque {};
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) E;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) c_int;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
 
 pub extern "c" fn umtx_sleep(ptr: *const volatile c_int, value: c_int, timeout: c_int) c_int;
 pub extern "c" fn umtx_wakeup(ptr: *const volatile c_int, count: c_int) c_int;
diff --git a/lib/std/c/emscripten.zig b/lib/std/c/emscripten.zig
index 501fcb4386b6..0893289b14a7 100644
--- a/lib/std/c/emscripten.zig
+++ b/lib/std/c/emscripten.zig
@@ -171,7 +171,7 @@ pub const RTLD = struct {
     pub const LOCAL = 0;
 };
 
-pub const dirent = struct {
+pub const dirent = extern struct {
     ino: c_uint,
     off: c_uint,
     reclen: c_ushort,
diff --git a/lib/std/c/linux.zig b/lib/std/c/linux.zig
index 1a3c63451502..6c3275274c64 100644
--- a/lib/std/c/linux.zig
+++ b/lib/std/c/linux.zig
@@ -318,8 +318,8 @@ pub const sem_t = extern struct {
 
 const __SIZEOF_SEM_T = 4 * @sizeOf(usize);
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) E;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8) c_int;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
 
 pub const RTLD = struct {
     pub const LAZY = 1;
@@ -330,14 +330,14 @@ pub const RTLD = struct {
     pub const LOCAL = 0;
 };
 
-pub const dirent = struct {
+pub const dirent = extern struct {
     ino: c_uint,
     off: c_uint,
     reclen: c_ushort,
     type: u8,
     name: [256]u8,
 };
-pub const dirent64 = struct {
+pub const dirent64 = extern struct {
     ino: c_ulong,
     off: c_ulong,
     reclen: c_ushort,
diff --git a/lib/std/c/netbsd.zig b/lib/std/c/netbsd.zig
index 3ec6de59b285..d7dfe4abe496 100644
--- a/lib/std/c/netbsd.zig
+++ b/lib/std/c/netbsd.zig
@@ -51,8 +51,8 @@ pub const pthread_attr_t = extern struct {
 
 pub const sem_t = ?*opaque {};
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*anyopaque) E;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*anyopaque) c_int;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
 
 pub const blkcnt_t = i64;
 pub const blksize_t = i32;
diff --git a/lib/std/c/solaris.zig b/lib/std/c/solaris.zig
index 4f08c32b0374..215dc417440d 100644
--- a/lib/std/c/solaris.zig
+++ b/lib/std/c/solaris.zig
@@ -34,8 +34,8 @@ pub const sem_t = extern struct {
     __pad2: [2]u64 = [_]u64{0} ** 2,
 };
 
-pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*anyopaque) E;
-pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) E;
+pub extern "c" fn pthread_setname_np(thread: std.c.pthread_t, name: [*:0]const u8, arg: ?*anyopaque) c_int;
+pub extern "c" fn pthread_getname_np(thread: std.c.pthread_t, name: [*:0]u8, len: usize) c_int;
 
 pub const blkcnt_t = i64;
 pub const blksize_t = i32;