diff --git a/src/header/grp/cbindgen.toml b/src/header/grp/cbindgen.toml
index 5383c8adf6..35dc5bcf32 100644
--- a/src/header/grp/cbindgen.toml
+++ b/src/header/grp/cbindgen.toml
@@ -2,7 +2,11 @@
 #
 # Spec quotations relating to includes:
 # - "The <grp.h> header shall define the gid_t and size_t types as described in <sys/types.h>."
-sys_includes = ["sys/types.h"]
+sys_includes = []
+after_includes = """
+#include <bits/gid-t.h>  // for gid_t from sys/types.h
+#include <bits/size-t.h> // for size_t from sys/types.h
+"""
 include_guard = "_RELIBC_GRP_H"
 language = "C"
 style = "Tag"
diff --git a/src/header/grp/mod.rs b/src/header/grp/mod.rs
index 3177c1bb36..60b4e5730c 100644
--- a/src/header/grp/mod.rs
+++ b/src/header/grp/mod.rs
@@ -84,6 +84,7 @@ static mut GROUP: group = group {
 static LINE_READER: SyncUnsafeCell<Option<Lines<BufReader<File>>>> = SyncUnsafeCell::new(None);
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/grp.h.html>.
+#[allow(non_camel_case_types)]
 #[repr(C)]
 #[derive(Debug)]
 pub struct group {
@@ -312,7 +313,7 @@ pub unsafe extern "C" fn getgrgid_r(
     gid: gid_t,
     result_buf: *mut group,
     buffer: *mut c_char,
-    buflen: usize,
+    buflen: size_t,
     result: *mut *mut group,
 ) -> c_int {
     // In case of error or the requested entry is not found.
@@ -373,7 +374,7 @@ pub unsafe extern "C" fn getgrnam_r(
     name: *const c_char,
     result_buf: *mut group,
     buffer: *mut c_char,
-    buflen: usize,
+    buflen: size_t,
     result: *mut *mut group,
 ) -> c_int {
     let Ok(db) = File::open(GROUP_FILE.into(), fcntl::O_RDONLY) else {