diff --git a/src/header/string/mod.rs b/src/header/string/mod.rs
index b4e27d80c3..315df2a770 100644
--- a/src/header/string/mod.rs
+++ b/src/header/string/mod.rs
@@ -20,20 +20,23 @@ use crate::{
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memccpy.html>.
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn memccpy(
-    dest: *mut c_void,
-    src: *const c_void,
+    s1: *mut c_void,
+    s2: *const c_void,
     c: c_int,
     n: size_t,
 ) -> *mut c_void {
-    let to = memchr(src, c, n);
+    let to = unsafe {memchr(s2, c, n)};
+    let dist = if to.is_null() {
+        n
+    } else {
+        ((to as usize) - (s2 as usize)) + 1
+    };
+    unsafe {memcpy(s1, s2, dist)};
     if to.is_null() {
-        return to;
+        ptr::null_mut()
+    } else {
+        unsafe {(s1 as *mut u8).add(dist) as *mut c_void}
     }
-    let dist = (to as usize) - (src as usize);
-    if memcpy(dest, src, dist).is_null() {
-        return ptr::null_mut();
-    }
-    (dest as *mut u8).add(dist + 1) as *mut c_void
 }
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memchr.html>.
@@ -53,7 +56,6 @@ pub unsafe extern "C" fn memchr(
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/memcmp.html>.
 #[unsafe(no_mangle)]
-#[unsafe(no_mangle)]
 pub unsafe extern "C" fn memcmp(s1: *const c_void, s2: *const c_void, n: usize) -> c_int {
     let (div, rem) = (n / mem::size_of::<usize>(), n % mem::size_of::<usize>());
     let mut a = s1 as *const usize;