diff --git a/components/style/properties/shorthand/background.mako.rs b/components/style/properties/shorthand/background.mako.rs
index 4e69dca81c3..8eaa94772f1 100644
--- a/components/style/properties/shorthand/background.mako.rs
+++ b/components/style/properties/shorthand/background.mako.rs
@@ -159,11 +159,17 @@
                 }
 
                 try!(image.to_css(dest));
-                % for name in "repeat attachment position_x position_y".split():
+                % for name in "repeat attachment".split():
                     try!(write!(dest, " "));
                     try!(${name}.to_css(dest));
                 % endfor
 
+                try!(write!(dest, " "));
+                Position {
+                    horizontal: position_x.clone(),
+                    vertical: position_y.clone()
+                }.to_css(dest)?;
+
                 if *size != background_size::single_value::get_initial_specified_value() {
                     try!(write!(dest, " / "));
                     try!(size.to_css(dest));
@@ -225,9 +231,11 @@
                 return Ok(());
             }
             for i in 0..len {
-                self.background_position_x.0[i].to_css(dest)?;
-                dest.write_str(" ")?;
-                self.background_position_y.0[i].to_css(dest)?;
+                Position {
+                    horizontal: self.background_position_x.0[i].clone(),
+                    vertical: self.background_position_y.0[i].clone()
+                }.to_css(dest)?;
+
                 if i < len - 1 {
                     dest.write_str(", ")?;
                 }
diff --git a/components/style/properties/shorthand/mask.mako.rs b/components/style/properties/shorthand/mask.mako.rs
index 8419a7d5951..8096f223757 100644
--- a/components/style/properties/shorthand/mask.mako.rs
+++ b/components/style/properties/shorthand/mask.mako.rs
@@ -148,9 +148,12 @@
                 dest.write_str(" ")?;
                 mode.to_css(dest)?;
                 dest.write_str(" ")?;
-                position_x.to_css(dest)?;
-                dest.write_str(" ")?;
-                position_y.to_css(dest)?;
+
+                Position {
+                    horizontal: position_x.clone(),
+                    vertical: position_y.clone()
+                }.to_css(dest)?;
+
                 if *size != mask_size::single_value::get_initial_specified_value() {
                     dest.write_str(" / ")?;
                     size.to_css(dest)?;
@@ -218,9 +221,11 @@
             }
 
             for i in 0..len {
-                self.mask_position_x.0[i].to_css(dest)?;
-                dest.write_str(" ")?;
-                self.mask_position_y.0[i].to_css(dest)?;
+                Position {
+                    horizontal: self.mask_position_x.0[i].clone(),
+                    vertical: self.mask_position_y.0[i].clone()
+                }.to_css(dest)?;
+
                 if i < len - 1 {
                     dest.write_str(", ")?;
                 }
diff --git a/components/style/values/specified/position.rs b/components/style/values/specified/position.rs
index 5c251cf54d5..edbe8c8472d 100644
--- a/components/style/values/specified/position.rs
+++ b/components/style/values/specified/position.rs
@@ -32,27 +32,36 @@ pub struct Position {
 
 impl ToCss for Position {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        let mut space_present = false;
-        if let Some(horiz_key) = self.horizontal.keyword {
-            try!(horiz_key.to_css(dest));
-            try!(dest.write_str(" "));
-            space_present = true;
-        };
-        if let Some(ref horiz_pos) = self.horizontal.position {
-            try!(horiz_pos.to_css(dest));
-            try!(dest.write_str(" "));
-            space_present = true;
-        };
-        if let Some(vert_key) = self.vertical.keyword {
-            try!(vert_key.to_css(dest));
-            space_present = false;
-        };
-        if let Some(ref vert_pos) = self.vertical.position {
-            if space_present == false {
-                try!(dest.write_str(" "));
-            }
-            try!(vert_pos.to_css(dest));
-        };
+        macro_rules! to_css_with_keyword {
+            ($pos:expr, $default_keyword:expr) => {
+                $pos.keyword.unwrap_or($default_keyword).to_css(dest)?;
+
+                if let Some(ref position) = $pos.position {
+                    dest.write_str(" ")?;
+                    position.to_css(dest)?;
+                };
+            };
+        }
+
+        let mut is_keyword_needed = false;
+        let position_x = &self.horizontal;
+        let position_y = &self.vertical;
+
+        if (position_x.keyword.is_some() && position_x.position.is_some()) ||
+           (position_y.keyword.is_some() && position_y.position.is_some()) {
+            is_keyword_needed = true;
+        }
+
+        if is_keyword_needed {
+            to_css_with_keyword!(position_x, Keyword::Left);
+            dest.write_str(" ")?;
+            to_css_with_keyword!(position_y, Keyword::Top);
+        } else {
+            position_x.to_css(dest)?;
+            dest.write_str(" ")?;
+            position_y.to_css(dest)?;
+        }
+
         Ok(())
     }
 }
@@ -403,6 +412,7 @@ impl ToCss for VerticalPosition {
         };
         Ok(())
     }
+
 }
 
 impl Parse for VerticalPosition {