diff --git a/src/mode/parser.rs b/src/mode/parser.rs
index 6727707..5c6f692 100644
--- a/src/mode/parser.rs
+++ b/src/mode/parser.rs
@@ -164,7 +164,7 @@ impl Parser {
 
     fn remove_bits(&mut self) {
         for bit in &self.bits {
-            self.mode &= *bit as u32;
+            self.mode &= !(*bit as u32);
         }
     }
 
@@ -175,9 +175,9 @@ impl Parser {
             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,
+                        Who::User => self.mode &= !0o4444,
+                        Who::Group => self.mode &= !0o2222,
+                        Who::Other => self.mode &= !0o1111,
                     }
                 }
                 self.add_bits();
@@ -238,3 +238,36 @@ impl Parser {
         Ok(self.mode)
     }
 }
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn add() {
+        let mut parser = Parser::new(0o644);
+        let mode = parser.parse("ug+x");
+        assert_eq!(mode, Ok(0o754));
+    }
+
+    #[test]
+    fn remove() {
+        let mut parser = Parser::new(0o777);
+        let mode = parser.parse("go-wx");
+        assert_eq!(mode, Ok(0o744));
+    }
+
+    #[test]
+    fn octal() {
+        let mut parser = Parser::default();
+        let mode = parser.parse("4755");
+        assert_eq!(mode, Ok(0o4755));
+    }
+
+    #[test]
+    fn equals() {
+        let mut parser = Parser::new(0o701);
+        let mode = parser.parse("ugo=rw");
+        assert_eq!(mode, Ok(0o666));
+    }
+}