diff --git a/src/mode/mod.rs b/src/mode/mod.rs
index b07b61a..320d556 100644
--- a/src/mode/mod.rs
+++ b/src/mode/mod.rs
@@ -8,7 +8,7 @@ pub fn get_umask() -> u32 {
     umask
 }
 
-#[derive(Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub enum Bit {
     Suid = 0o4000,
     Sgid = 0o2000,
diff --git a/src/mode/parser.rs b/src/mode/parser.rs
index 7a5ad18..6727707 100644
--- a/src/mode/parser.rs
+++ b/src/mode/parser.rs
@@ -36,14 +36,13 @@ enum Who {
     User,
     Group,
     Other,
-    All,
 }
 
 pub struct Parser {
     mode: u32,
     op: Option<Op>,
     who: Vec<Who>,
-    bits: Vec<char>,
+    bits: Vec<Bit>,
 }
 
 impl Default for Parser {
@@ -97,175 +96,95 @@ impl Parser {
         }
     }
 
-    fn push_bit(&mut self, bit: char) -> Result<(), ParseError> {
-        match self.op {
-            Some(_) => if self.bits.contains(&bit) {
-                return Err(ParseError::InvalidDigit);
-            } else {
-                self.bits.push(bit);
-            },
-            None => return Err(ParseError::NoOpSet),
+    fn push_read_bits(&mut self) -> Result<(), ParseError> {
+        for w in &self.who {
+            match w {
+                Who::User => self.bits.push(Bit::URead),
+                Who::Group => self.bits.push(Bit::GRead),
+                Who::Other => self.bits.push(Bit::ORead),
+            }
         }
         Ok(())
     }
 
-    fn push_suid(&mut self) -> Result<(), ParseError> {
+    fn push_write_bits(&mut self) -> Result<(), ParseError> {
         for w in &self.who {
-            if w == &Who::All || w == &Who::Other {
-                return Err(ParseError::InvalidBit);
+            match w {
+                Who::User => self.bits.push(Bit::UWrite),
+                Who::Group => self.bits.push(Bit::GWrite),
+                Who::Other => self.bits.push(Bit::OWrite),
             }
         }
+        Ok(())
+    }
+
+    fn push_exec_bits(&mut self) -> Result<(), ParseError> {
+        for w in &self.who {
+            match w {
+                Who::User => self.bits.push(Bit::UExec),
+                Who::Group => self.bits.push(Bit::GExec),
+                Who::Other => self.bits.push(Bit::OExec),
+            }
+        }
+        Ok(())
+    }
+
+    fn push_suid_sgid(&mut self) -> Result<(), ParseError> {
         if self.who.is_empty() {
             return Err(ParseError::InvalidBit);
         }
-        self.push_bit('s')
+        for w in &self.who {
+            match w {
+                &Who::Other => return Err(ParseError::InvalidBit),
+                &Who::User => self.bits.push(Bit::Suid),
+                &Who::Group => self.bits.push(Bit::Sgid),
+            }
+        }
+        Ok(())
     }
 
     fn push_sticky(&mut self) -> Result<(), ParseError> {
-        for w in &self.who {
-            if w == &Who::All || w == &Who::User || w == &Who::Group {
-                return Err(ParseError::InvalidBit);
-            }
-        }
         if self.who.is_empty() {
             return Err(ParseError::InvalidBit);
         }
-        self.push_bit('t')
-    }
-
-    fn add_user_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode |= Bit::URead as u32,
-                'w' => self.mode |= Bit::UWrite as u32,
-                'x' => self.mode |= Bit::UExec as u32,
-                's' => self.mode |= Bit::Suid as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn remove_user_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode &= Bit::URead as u32,
-                'w' => self.mode &= Bit::UWrite as u32,
-                'x' => self.mode &= Bit::UExec as u32,
-                's' => self.mode &= Bit::Suid as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn zero_user_bits(&mut self) {
-        self.mode &= 0o4444;
-    }
-
-    fn set_user_bits(&mut self) {
-        match self.op {
-            Some(Op::Add) => self.add_user_bits(),
-            Some(Op::Remove) => self.remove_user_bits(),
-            Some(Op::Equals) => {
-                self.zero_user_bits();
-                self.add_user_bits();
-            },
-            None => {},
-        }
-    }
-
-    fn add_group_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode |= Bit::GRead as u32,
-                'w' => self.mode |= Bit::GWrite as u32,
-                'x' => self.mode |= Bit::GExec as u32,
-                's' => self.mode |= Bit::Sgid as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn remove_group_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode &= Bit::GRead as u32,
-                'w' => self.mode &= Bit::GWrite as u32,
-                'x' => self.mode &= Bit::GExec as u32,
-                's' => self.mode &= Bit::Sgid as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn zero_group_bits(&mut self) {
-        self.mode &= 0o2222;
-    }
-
-    fn set_group_bits(&mut self) {
-        match self.op {
-            Some(Op::Add) => self.add_group_bits(),
-            Some(Op::Remove) => self.remove_group_bits(),
-            Some(Op::Equals) => {
-                self.zero_group_bits();
-                self.add_group_bits();
-            },
-            None => {},
-        }
-    }
-
-    fn add_other_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode |= Bit::ORead as u32,
-                'w' => self.mode |= Bit::OWrite as u32,
-                'x' => self.mode |= Bit::OExec as u32,
-                't' => self.mode |= Bit::Sticky as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn remove_other_bits(&mut self) {
-        for b in &self.bits {
-            match b {
-                'r' => self.mode &= Bit::ORead as u32,
-                'w' => self.mode &= Bit::OWrite as u32,
-                'x' => self.mode &= Bit::OExec as u32,
-                's' => self.mode &= Bit::Sticky as u32,
-                _ => unreachable!(),
-            }
-        }
-    }
-
-    fn zero_other_bits(&mut self) {
-        self.mode &= 0o1111;
-    }
-
-    fn set_other_bits(&mut self) {
-        match self.op {
-            Some(Op::Add) => self.add_other_bits(),
-            Some(Op::Remove) => self.remove_other_bits(),
-            Some(Op::Equals) => {
-                self.zero_other_bits();
-                self.add_other_bits();
-            },
-            None => {},
-        }
-    }
-
-    fn set_bits(&mut self) {
-        for w in self.who.clone() {
+        for w in &self.who {
             match w {
-                Who::User => self.set_user_bits(),
-                Who::Group => self.set_group_bits(),
-                Who::Other => self.set_other_bits(),
-                Who::All => {
-                    self.set_user_bits();
-                    self.set_group_bits();
-                    self.set_other_bits();
-                }
+                &Who::User | &Who::Group => return Err(ParseError::InvalidBit),
+                &Who::Other => self.bits.push(Bit::Sticky),
             }
         }
+        Ok(())
+    }
+
+    fn add_bits(&mut self) {
+        for bit in &self.bits {
+            self.mode |= *bit as u32;
+        }
+    }
+
+    fn remove_bits(&mut self) {
+        for bit in &self.bits {
+            self.mode &= *bit as u32;
+        }
+    }
+
+    fn set_bits(&mut self) -> Result<(), ParseError> {
+        match self.op {
+            Some(Op::Add) => self.add_bits(),
+            Some(Op::Remove) => self.remove_bits(),
+            Some(Op::Equals) => {
+                for w in &self.who {
+                    match w {
+                        Who::User => self.mode &= 0o4444,
+                        Who::Group => self.mode &= 0o2222,
+                        Who::Other => self.mode &= 0o1111,
+                    }
+                }
+                self.add_bits();
+            },
+            None => return Err(ParseError::NoOpSet),
+        }
+        Ok(())
     }
 
     fn reset(&mut self) {
@@ -293,17 +212,28 @@ impl Parser {
                 'u' => self.add_who(Who::User)?,
                 'g' => self.add_who(Who::Group)?,
                 'o' => self.add_who(Who::Other)?,
-                'a' => self.add_who(Who::All)?,
+                'a' => {
+                    self.add_who(Who::User)?;
+                    self.add_who(Who::Group)?;
+                    self.add_who(Who::Other)?;
+                },
                 '-' => self.set_op(Op::Remove)?,
                 '+' => self.set_op(Op::Add)?,
                 '=' => self.set_op(Op::Equals)?,
-                'r' | 'w' | 'x' => self.push_bit(c)?,
-                's' => self.push_suid()?,
+                'r' => self.push_read_bits()?,
+                'w' => self.push_write_bits()?,
+                'x' => self.push_exec_bits()?,
+                's' => self.push_suid_sgid()?,
                 't' => self.push_sticky()?,
                 _ => return Err(ParseError::InvalidDigit),
             }
         }
-        self.set_bits();
+        if self.who.is_empty() {
+            self.who.push(Who::User);
+            self.who.push(Who::Group);
+            self.who.push(Who::Other);
+        }
+        self.set_bits()?;
         self.reset();
         Ok(self.mode)
     }