diff --git a/common/c_types.rs b/common/c_types.rs
index 000669154..fec14f4e5 100644
--- a/common/c_types.rs
+++ b/common/c_types.rs
@@ -13,6 +13,7 @@ use self::libc::funcs::posix88::unistd::getgroups;
 
 use std::vec::Vec;
 
+use std::io::IoError;
 use std::ptr::read;
 use std::str::raw::from_c_str;
 
@@ -20,8 +21,8 @@ use std::str::raw::from_c_str;
 pub struct c_passwd {
     pub pw_name:    *c_char,    /* user name */
     pub pw_passwd:  *c_char,    /* user name */
-    pub pw_uid:     c_int,      /* user uid */
-    pub pw_gid:     c_int,      /* user gid */
+    pub pw_uid:     uid_t,      /* user uid */
+    pub pw_gid:     gid_t,      /* user gid */
     pub pw_change:  time_t,
     pub pw_class:   *c_char,
     pub pw_gecos:   *c_char,
@@ -34,8 +35,8 @@ pub struct c_passwd {
 pub struct c_passwd {
     pub pw_name:    *c_char,    /* user name */
     pub pw_passwd:  *c_char,    /* user name */
-    pub pw_uid:     c_int,      /* user uid */
-    pub pw_gid:     c_int,      /* user gid */
+    pub pw_uid:     uid_t,      /* user uid */
+    pub pw_gid:     gid_t,      /* user gid */
     pub pw_gecos:   *c_char,
     pub pw_dir:     *c_char,
     pub pw_shell:   *c_char,
@@ -80,13 +81,13 @@ pub struct c_tm {
 }
 
 extern {
-    pub fn getpwuid(uid: c_int) -> *c_passwd;
+    pub fn getpwuid(uid: uid_t) -> *c_passwd;
     pub fn getpwnam(login: *c_char) -> *c_passwd;
     pub fn getgrouplist(name:   *c_char,
-                        basegid: c_int,
-                        groups: *c_int,
+                        basegid: gid_t,
+                        groups: *gid_t,
                         ngroups: *mut c_int) -> c_int;
-    pub fn getgrgid(gid: uid_t) -> *c_group;
+    pub fn getgrgid(gid: gid_t) -> *c_group;
 }
 
 pub fn get_pw_from_args(free: &Vec<String>) -> Option<c_passwd> {
@@ -95,8 +96,8 @@ pub fn get_pw_from_args(free: &Vec<String>) -> Option<c_passwd> {
 
         // Passed user as id
         if username.chars().all(|c| c.is_digit()) {
-            let id = from_str::<i32>(username).unwrap();
-            let pw_pointer = unsafe { getpwuid(id) };
+            let id = from_str::<u32>(username).unwrap();
+            let pw_pointer = unsafe { getpwuid(id as uid_t) };
 
             if pw_pointer.is_not_null() {
                 Some(unsafe { read(pw_pointer) })
@@ -137,16 +138,19 @@ pub fn group(possible_pw: Option<c_passwd>, nflag: bool) {
         }
     } else {
         ngroups = unsafe {
-            getgroups(NGROUPS, groups.as_mut_ptr() as *mut u32)
+            getgroups(NGROUPS, groups.as_mut_ptr() as *mut gid_t)
         };
     }
 
+    if ngroups < 0 {
+        crash!(1, "{}", IoError::last_error());
+    }
 
     unsafe { groups.set_len(ngroups as uint) };
 
     for &g in groups.iter() {
         if nflag {
-            let group = unsafe { getgrgid(g as u32) };
+            let group = unsafe { getgrgid(g) };
             if group.is_not_null() {
                 let name = unsafe {
                     from_c_str(read(group).gr_name)
@@ -154,7 +158,7 @@ pub fn group(possible_pw: Option<c_passwd>, nflag: bool) {
                 print!("{:s} ", name);
             }
         } else {
-            print!("{:d} ", g);
+            print!("{:u} ", g);
         }
     }
 
diff --git a/id/id.rs b/id/id.rs
index 785f6d2ec..4bd97943a 100644
--- a/id/id.rs
+++ b/id/id.rs
@@ -23,6 +23,7 @@ use std::ptr::read;
 use libc::{
     c_char,
     c_int,
+    gid_t,
     uid_t,
     getgid,
     getuid
@@ -80,8 +81,8 @@ mod audit {
 extern {
     fn getgrgid(gid: uid_t) -> *c_group;
     fn getgrouplist(name:   *c_char,
-                    basegid: c_int,
-                    groups: *c_int,
+                    basegid: gid_t,
+                    groups: *gid_t,
                     ngroups: *mut c_int) -> c_int;
 }
 
@@ -136,11 +137,11 @@ pub fn uumain(args: Vec<String>) -> int {
             possible_pw.unwrap().pw_gid
         } else {
             if rflag {
-                unsafe { getgid() as i32 }
+                unsafe { getgid() }
             } else {
-                unsafe { getegid() as i32 }
+                unsafe { getegid() }
             }
-        } as u32;
+        };
         let gr = unsafe { getgrgid(id) };
 
         if nflag && gr.is_not_null() {
@@ -156,9 +157,9 @@ pub fn uumain(args: Vec<String>) -> int {
         let id = if possible_pw.is_some() {
             possible_pw.unwrap().pw_uid
         } else if rflag {
-            unsafe { getgid() as i32 }
+            unsafe { getgid() }
         } else {
-            unsafe { getegid() as i32 }
+            unsafe { getegid() }
         };
 
         let pw = unsafe { getpwuid(id) };
@@ -168,7 +169,7 @@ pub fn uumain(args: Vec<String>) -> int {
             };
             println!("{:s}", pw_name);
         } else {
-            println!("{:d}", id);
+            println!("{:u}", id);
         }
 
         return 0;
@@ -208,7 +209,7 @@ fn pretty(possible_pw: Option<c_passwd>) {
     } else {
         let login = unsafe { from_c_str(getlogin()) };
         let rid = unsafe { getuid() };
-        let pw = unsafe { getpwuid(rid as i32) };
+        let pw = unsafe { getpwuid(rid) };
 
         let is_same_user = unsafe {
             from_c_str(read(pw).pw_name) == login
@@ -228,7 +229,7 @@ fn pretty(possible_pw: Option<c_passwd>) {
 
         let eid = unsafe { getegid() };
         if eid == rid {
-            let pw = unsafe { getpwuid(eid as i32) };
+            let pw = unsafe { getpwuid(eid) };
             if pw.is_not_null() {
                 println!(
                     "euid\t{:s}",
@@ -288,7 +289,7 @@ fn pline(possible_pw: Option<c_passwd>) {
 #[cfg(target_os = "linux")]
 fn pline(possible_pw: Option<c_passwd>) {
     let pw = if possible_pw.is_none() {
-        unsafe { read(getpwuid(getuid() as i32)) }
+        unsafe { read(getpwuid(getuid())) }
     } else {
         possible_pw.unwrap()
     };
@@ -300,7 +301,7 @@ fn pline(possible_pw: Option<c_passwd>) {
     let pw_shell    = unsafe { from_c_str(pw.pw_shell) };
 
     println!(
-        "{:s}:{:s}:{:d}:{:d}:{:s}:{:s}:{:s}",
+        "{:s}:{:s}:{:u}:{:u}:{:s}:{:s}:{:s}",
         pw_name,
         pw_passwd,
         pw.pw_uid,
@@ -343,8 +344,8 @@ fn id_print(possible_pw: Option<c_passwd>,
         uid = possible_pw.unwrap().pw_uid;
         gid = possible_pw.unwrap().pw_gid;
     } else {
-        uid = unsafe { getuid() as i32 };
-        gid = unsafe { getgid() as i32 };
+        uid = unsafe { getuid() };
+        gid = unsafe { getgid() };
     }
 
     let mut ngroups;
@@ -363,15 +364,15 @@ fn id_print(possible_pw: Option<c_passwd>,
 
     if possible_pw.is_some() {
         print!(
-            "uid={:d}({:s})",
+            "uid={:u}({:s})",
             uid,
             unsafe { from_c_str(possible_pw.unwrap().pw_name) });
     } else {
         print!("uid={:u}", unsafe { getuid() });
     }
 
-    print!(" gid={:d}", gid);
-    let gr = unsafe { getgrgid(gid as u32) };
+    print!(" gid={:u}", gid);
+    let gr = unsafe { getgrgid(gid) };
     if gr.is_not_null() {
         print!(
             "({:s})",
@@ -379,9 +380,9 @@ fn id_print(possible_pw: Option<c_passwd>,
     }
 
     let euid = unsafe { geteuid() };
-    if p_euid && (euid != uid as u32) {
+    if p_euid && (euid != uid) {
         print!(" euid={:u}", euid);
-        let pw = unsafe { getpwuid(euid as i32) };
+        let pw = unsafe { getpwuid(euid) };
         if pw.is_not_null() {
             print!(
                 "({:s})",
@@ -408,7 +409,7 @@ fn id_print(possible_pw: Option<c_passwd>,
         let mut first = true;
         for &gr in groups.iter() {
             if !first { print!(",") }
-            print!("{:d}", gr);
+            print!("{:u}", gr);
             let group = unsafe { getgrgid(gr as u32) };
             if group.is_not_null() {
                 let name = unsafe {
diff --git a/whoami/whoami.rs b/whoami/whoami.rs
index cedb32778..4abe953e7 100644
--- a/whoami/whoami.rs
+++ b/whoami/whoami.rs
@@ -32,7 +32,7 @@ mod platform {
     #[path = "../../common/c_types.rs"] mod c_types;
 
     extern {
-        pub fn geteuid() -> libc::c_int;
+        pub fn geteuid() -> libc::uid_t;
     }
 
     pub unsafe fn getusername() -> String {