diff --git a/src/header/fmtmsg/mod.rs b/src/header/fmtmsg/mod.rs
index 235ea40068..56e983e5c2 100644
--- a/src/header/fmtmsg/mod.rs
+++ b/src/header/fmtmsg/mod.rs
@@ -77,7 +77,7 @@ unsafe fn strcolcmp(mut lstr: *const c_char, mut bstr: *const c_char) -> c_int {
             lstr = lstr.add(1);
             bstr = bstr.add(1);
         }
-        if *lstr != 0 || (*bstr != 0 && *bstr != b':' as c_char) {
+        if *lstr != 0 || (*bstr != 0 && *bstr != b':'.cast_signed()) {
             1
         } else {
             0
diff --git a/src/header/getopt/mod.rs b/src/header/getopt/mod.rs
index 1cc310a677..bf003e4191 100644
--- a/src/header/getopt/mod.rs
+++ b/src/header/getopt/mod.rs
@@ -61,7 +61,7 @@ pub unsafe extern "C" fn getopt_long(
             let current_arg = unsafe { *argv.offset(optind as isize) };
             if unsafe {
                 current_arg.is_null()
-                    || *current_arg != b'-' as c_char
+                    || *current_arg != b'-'.cast_signed()
                     || *current_arg.offset(1) == 0
             } {
                 -1
@@ -74,7 +74,7 @@ pub unsafe extern "C" fn getopt_long(
                 // remove the '-'
                 let current_arg = unsafe { current_arg.offset(1) };
 
-                if unsafe { *current_arg == b'-' as c_char } && !longopts.is_null() {
+                if unsafe { *current_arg == b'-'.cast_signed() } && !longopts.is_null() {
                     let current_arg = unsafe { current_arg.offset(1) };
                     // is a long option
                     for i in 0.. {
@@ -86,7 +86,7 @@ pub unsafe extern "C" fn getopt_long(
                         let mut end = 0;
                         while {
                             let c = unsafe { *current_arg.offset(end) };
-                            c != 0 && c != b'=' as c_char
+                            c != 0 && c != b'='.cast_signed()
                         } {
                             end += 1;
                         }
@@ -101,18 +101,18 @@ pub unsafe extern "C" fn getopt_long(
 
                             if opt.has_arg == optional_argument {
                                 unsafe {
-                                    if *current_arg.offset(end) == b'=' as c_char {
+                                    if *current_arg.offset(end) == b'='.cast_signed() {
                                         optarg = current_arg.offset(end + 1);
                                     }
                                 }
                             } else if opt.has_arg == required_argument {
                                 unsafe {
-                                    if *current_arg.offset(end) == b'=' as c_char {
+                                    if *current_arg.offset(end) == b'='.cast_signed() {
                                         optarg = current_arg.offset(end + 1);
                                     } else if optind < argc {
                                         optarg = *argv.offset(optind as isize);
                                         optind += 1;
-                                    } else if *optstring == b':' as c_char {
+                                    } else if *optstring == b':'.cast_signed() {
                                         return c_int::from(b':');
                                     } else {
                                         stdio::fputs((*argv).cast_const(), &raw mut *stdio::stderr);
@@ -183,7 +183,7 @@ unsafe fn parse_arg(
                     CURRENT_OPT = ptr::null_mut();
 
                     optopt = c_int::from(*current_arg);
-                    let errch = if *optstring == b':' as c_char {
+                    let errch = if *optstring == b':'.cast_signed() {
                         b':'
                     } else {
                         if opterr != 0 {
@@ -231,7 +231,7 @@ unsafe fn find_option(ch: c_char, optstring: *const c_char) -> Option<GetoptOpti
 
     while unsafe { *optstring.offset(i) != 0 } {
         if unsafe { *optstring.offset(i) == ch } {
-            let result = if unsafe { *optstring.offset(i + 1) == b':' as c_char } {
+            let result = if unsafe { *optstring.offset(i + 1) == b':'.cast_signed() } {
                 GetoptOption::OptArg
             } else {
                 GetoptOption::Flag
diff --git a/src/header/libgen/mod.rs b/src/header/libgen/mod.rs
index a4e39c7584..0a3fc0710a 100644
--- a/src/header/libgen/mod.rs
+++ b/src/header/libgen/mod.rs
@@ -13,14 +13,14 @@ pub unsafe extern "C" fn basename(str: *mut c_char) -> *mut c_char {
         return c".".as_ptr().cast_mut();
     }
     let mut end = unsafe { strlen(str) as isize - 1 };
-    while end >= 0 && unsafe { *str.offset(end) == b'/' as c_char } {
+    while end >= 0 && unsafe { *str.offset(end) == b'/'.cast_signed() } {
         end -= 1;
     }
     if end == -1 {
         return c"/".as_ptr().cast_mut();
     }
     let mut begin = end;
-    while begin >= 0 && unsafe { *str.offset(begin) != b'/' as c_char } {
+    while begin >= 0 && unsafe { *str.offset(begin) != b'/'.cast_signed() } {
         begin -= 1;
     }
     unsafe {
@@ -36,13 +36,13 @@ pub unsafe extern "C" fn dirname(str: *mut c_char) -> *mut c_char {
         return c".".as_ptr().cast_mut();
     }
     let mut end = unsafe { strlen(str) as isize - 1 };
-    while end > 0 && unsafe { *str.offset(end) == b'/' as c_char } {
+    while end > 0 && unsafe { *str.offset(end) == b'/'.cast_signed() } {
         end -= 1;
     }
-    while end >= 0 && unsafe { *str.offset(end) != b'/' as c_char } {
+    while end >= 0 && unsafe { *str.offset(end) != b'/'.cast_signed() } {
         end -= 1;
     }
-    while end > 0 && unsafe { *str.offset(end) == b'/' as c_char } {
+    while end > 0 && unsafe { *str.offset(end) == b'/'.cast_signed() } {
         end -= 1;
     }
     if end == -1 {
diff --git a/src/header/locale/mod.rs b/src/header/locale/mod.rs
index d8f9e54bd3..b6dd7aa33f 100644
--- a/src/header/locale/mod.rs
+++ b/src/header/locale/mod.rs
@@ -15,7 +15,7 @@ use crate::{
 };
 
 // Can't use &str because of the mutability
-static mut C_LOCALE: [c_char; 2] = [b'C' as c_char, 0];
+static mut C_LOCALE: [c_char; 2] = [b'C'.cast_signed(), 0];
 
 mod constants;
 use constants::*;
diff --git a/src/header/stdio/mod.rs b/src/header/stdio/mod.rs
index 93e717c827..11e18a428b 100644
--- a/src/header/stdio/mod.rs
+++ b/src/header/stdio/mod.rs
@@ -553,9 +553,9 @@ pub unsafe extern "C" fn flockfile(file: *mut FILE) {
 #[unsafe(no_mangle)]
 pub unsafe extern "C" fn fopen(filename: *const c_char, mode: *const c_char) -> *mut FILE {
     let initial_mode = unsafe { *mode };
-    if initial_mode != b'r' as c_char
-        && initial_mode != b'w' as c_char
-        && initial_mode != b'a' as c_char
+    if initial_mode != b'r'.cast_signed()
+        && initial_mode != b'w'.cast_signed()
+        && initial_mode != b'a'.cast_signed()
     {
         platform::ERRNO.set(errno::EINVAL);
         return ptr::null_mut();
@@ -1291,7 +1291,7 @@ pub unsafe extern "C" fn tempnam(dir: *const c_char, pfx: *const c_char) -> *mut
     if !out_buf.is_null() {
         // copy the directory name and prefix into the allocated buffer
         unsafe { out_buf.copy_from_nonoverlapping(dirname, dirname_len) };
-        unsafe { *out_buf.add(dirname_len) = b'/' as _ };
+        unsafe { *out_buf.add(dirname_len) = b'/'.cast_signed() };
         unsafe {
             out_buf
                 .add(dirname_len + 1)
@@ -1350,7 +1350,7 @@ pub unsafe extern "C" fn tmpnam(s: *mut c_char) -> *mut c_char {
         s
     };
 
-    unsafe { *buf = b'/' as _ };
+    unsafe { *buf = b'/'.cast_signed() };
     unsafe {
         #[allow(deprecated)]
         tmpnam_inner(buf, 1)
diff --git a/src/header/stdlib/mod.rs b/src/header/stdlib/mod.rs
index 5477101ea1..ee7a3c1026 100644
--- a/src/header/stdlib/mod.rs
+++ b/src/header/stdlib/mod.rs
@@ -421,13 +421,13 @@ unsafe fn find_env(search: *const c_char) -> Option<(usize, *mut c_char)> {
     for (i, mut item) in platform::environ_iter().enumerate() {
         let mut search = search;
         loop {
-            let end_of_query = unsafe { *search } == 0 || unsafe { *search } == b'=' as c_char;
+            let end_of_query = unsafe { *search } == 0 || unsafe { *search } == b'='.cast_signed();
             if unsafe { *item } == 0 {
                 //TODO: environ has an item without value, is this a problem?
                 break;
             }
-            if unsafe { *item } == b'=' as c_char || end_of_query {
-                if unsafe { *item } == b'=' as c_char && end_of_query {
+            if unsafe { *item } == b'='.cast_signed() || end_of_query {
+                if unsafe { *item } == b'='.cast_signed() && end_of_query {
                     // Both keys env here
                     return Some((i, unsafe { item.add(1) }));
                 } else {
@@ -475,7 +475,7 @@ pub unsafe extern "C" fn getsubopt(
     let mut found_comma = false;
 
     while unsafe { *cursor } != 0 {
-        if unsafe { *cursor } == b',' as c_char {
+        if unsafe { *cursor } == b','.cast_signed() {
             unsafe { *cursor = 0 };
             unsafe { *optionp = cursor.add(1) };
             found_comma = true;
@@ -496,7 +496,7 @@ pub unsafe extern "C" fn getsubopt(
         if unsafe { strncmp(start, token, token_len) } == 0 {
             let suffix_char = unsafe { *start.add(token_len) };
 
-            if suffix_char == b'=' as c_char {
+            if suffix_char == b'='.cast_signed() {
                 unsafe { *valuep = start.add(token_len + 1) };
                 return i as c_int;
             } else if suffix_char == 0 {
@@ -754,7 +754,7 @@ where
     }
 
     for i in (len - suffix_len - 6)..(len - suffix_len) {
-        if unsafe { *name.offset(i as isize) } != b'X' as c_char {
+        if unsafe { *name.offset(i as isize) } != b'X'.cast_signed() {
             platform::ERRNO.set(errno::EINVAL);
             return None;
         }
@@ -1258,7 +1258,7 @@ unsafe fn copy_kv(
     value_len: usize,
 ) {
     unsafe { core::ptr::copy_nonoverlapping(key, existing, key_len) };
-    unsafe { core::ptr::write(existing.add(key_len), b'=' as c_char) };
+    unsafe { core::ptr::write(existing.add(key_len), b'='.cast_signed()) };
     unsafe { core::ptr::copy_nonoverlapping(value, existing.add(key_len + 1), value_len) };
     unsafe { core::ptr::write(existing.add(key_len + 1 + value_len), 0) };
 }
@@ -1365,8 +1365,8 @@ pub unsafe extern "C" fn srandom(seed: c_uint) {
 pub fn is_positive(ch: c_char) -> Option<(bool, isize)> {
     match ch {
         0 => None,
-        ch if ch == b'+' as c_char => Some((true, 1)),
-        ch if ch == b'-' as c_char => Some((false, 1)),
+        ch if ch == b'+'.cast_signed() => Some((true, 1)),
+        ch if ch == b'-'.cast_signed() => Some((false, 1)),
         _ => Some((true, 0)),
     }
 }
@@ -1391,7 +1391,7 @@ pub unsafe fn detect_base(s: *const c_char) -> Option<(c_int, isize)> {
 }
 
 pub unsafe fn convert_octal(s: *const c_char) -> Option<(c_ulong, isize, bool)> {
-    if unsafe { *s } != 0 && unsafe { *s } == b'0' as c_char {
+    if unsafe { *s } != 0 && unsafe { *s } == b'0'.cast_signed() {
         if let Some((val, idx, overflow)) = unsafe { convert_integer(s.offset(1), 8) } {
             Some((val, idx + 1, overflow))
         } else {
@@ -1404,10 +1404,10 @@ pub unsafe fn convert_octal(s: *const c_char) -> Option<(c_ulong, isize, bool)>
 }
 
 pub unsafe fn convert_hex(s: *const c_char) -> Option<(c_ulong, isize, bool)> {
-    if (unsafe { *s } != 0 && unsafe { *s } == b'0' as c_char)
+    if (unsafe { *s } != 0 && unsafe { *s } == b'0'.cast_signed())
         && (unsafe { *s.offset(1) } != 0
-            && (unsafe { *s.offset(1) } == b'x' as c_char
-                || unsafe { *s.offset(1) } == b'X' as c_char))
+            && (unsafe { *s.offset(1) } == b'x'.cast_signed()
+                || unsafe { *s.offset(1) } == b'X'.cast_signed()))
     {
         unsafe { convert_integer(s.offset(2), 16) }
             .map(|(val, idx, overflow)| (val, idx + 2, overflow))