diff --git a/src/header/arpa_inet/mod.rs b/src/header/arpa_inet/mod.rs
index efd0ad39a7..69df751967 100644
--- a/src/header/arpa_inet/mod.rs
+++ b/src/header/arpa_inet/mod.rs
@@ -118,16 +118,18 @@ pub unsafe extern "C" fn inet_network(cp: *const c_char) -> in_addr_t {
 /// Specifications Issue 8.
 #[deprecated]
 #[unsafe(no_mangle)]
-pub unsafe extern "C" fn inet_ntoa(r#in: in_addr) -> *const c_char {
+pub unsafe extern "C" fn inet_ntoa(r#in: in_addr) -> *mut c_char {
     static NTOA_ADDR: RawCell<[c_char; 16]> = RawCell::new([0; 16]);
 
     unsafe {
-        inet_ntop(
+        let ptr = inet_ntop(
             AF_INET,
             &r#in as *const in_addr as *const c_void,
             NTOA_ADDR.unsafe_mut().as_mut_ptr(),
             NTOA_ADDR.unsafe_ref().len() as socklen_t,
-        )
+        );
+        // Mutable pointer is required, inet_ntop returns destination as const pointer
+        ptr as *mut c_char
     }
 }
 
diff --git a/src/header/langinfo/mod.rs b/src/header/langinfo/mod.rs
index 6094b0f5e3..0a9c265b73 100644
--- a/src/header/langinfo/mod.rs
+++ b/src/header/langinfo/mod.rs
@@ -139,13 +139,16 @@ pub const CRNCYSTR: nl_item = 56;
 /// # Safety
 /// - Caller must ensure `item` is a valid `nl_item` index.
 /// - Returns a pointer to a null-terminated string, or an empty string if the item is invalid.
+/// - Compatibility requires mutable pointer to be returned, but it should not be mutated!
 #[unsafe(no_mangle)]
-pub unsafe extern "C" fn nl_langinfo(item: nl_item) -> *const c_char {
+pub unsafe extern "C" fn nl_langinfo(item: nl_item) -> *mut c_char {
     // Validate the item and perform the lookup
-    if (item as usize) < STRING_TABLE.len() {
+    let ptr = if (item as usize) < STRING_TABLE.len() {
         STRING_TABLE[item as usize].as_ptr() as *const c_char
     } else {
         // Return a pointer to an empty string if the item is invalid
         b"\0".as_ptr() as *const c_char
-    }
+    };
+    // Mutable pointer is required (unsafe!)
+    ptr as *mut c_char
 }
diff --git a/src/header/time/mod.rs b/src/header/time/mod.rs
index 2d183ba78d..d82228bcd9 100644
--- a/src/header/time/mod.rs
+++ b/src/header/time/mod.rs
@@ -543,7 +543,7 @@ pub unsafe extern "C" fn timelocal(tm: *mut tm) -> time_t {
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn timer_create(
     clock_id: clockid_t,
-    evp: *const sigevent,
+    evp: *mut sigevent,
     timerid: *mut timer_t,
 ) -> c_int {
     if evp.is_null() || timerid.is_null() {
diff --git a/src/header/unistd/mod.rs b/src/header/unistd/mod.rs
index 28acfb6efc..590546ddbd 100644
--- a/src/header/unistd/mod.rs
+++ b/src/header/unistd/mod.rs
@@ -835,7 +835,7 @@ pub unsafe extern "C" fn pwrite(
 
 /// See <https://pubs.opengroup.org/onlinepubs/9799919799/functions/read.html>.
 #[unsafe(no_mangle)]
-pub unsafe extern "C" fn read(fildes: c_int, buf: *const c_void, nbyte: size_t) -> ssize_t {
+pub unsafe extern "C" fn read(fildes: c_int, buf: *mut c_void, nbyte: size_t) -> ssize_t {
     let buf = unsafe { slice::from_raw_parts_mut(buf as *mut u8, nbyte as usize) };
     trace_expr!(
         Sys::read(fildes, buf)