diff --git a/components/fonts/font.rs b/components/fonts/font.rs
index 67236debef1..14c55b928de 100644
--- a/components/fonts/font.rs
+++ b/components/fonts/font.rs
@@ -12,6 +12,7 @@ use std::{iter, str};
 use app_units::Au;
 use bitflags::bitflags;
 use euclid::default::{Point2D, Rect, Size2D};
+use euclid::num::Zero;
 use log::debug;
 use malloc_size_of_derive::MallocSizeOf;
 use parking_lot::RwLock;
@@ -137,6 +138,9 @@ pub struct FontMetrics {
     pub line_gap: Au,
     pub zero_horizontal_advance: Option<Au>,
     pub ic_horizontal_advance: Option<Au>,
+    /// The advance of the space character (' ') in this font or if there is no space,
+    /// the average char advance.
+    pub space_advance: Au,
 }
 
 impl FontMetrics {
@@ -144,20 +148,21 @@ impl FontMetrics {
     /// no font can be found.
     pub fn empty() -> Self {
         Self {
-            underline_size: Au(0),
-            underline_offset: Au(0),
-            strikeout_size: Au(0),
-            strikeout_offset: Au(0),
-            leading: Au(0),
-            x_height: Au(0),
-            em_size: Au(0),
-            ascent: Au(0),
-            descent: Au(0),
-            max_advance: Au(0),
-            average_advance: Au(0),
-            line_gap: Au(0),
+            underline_size: Au::zero(),
+            underline_offset: Au::zero(),
+            strikeout_size: Au::zero(),
+            strikeout_offset: Au::zero(),
+            leading: Au::zero(),
+            x_height: Au::zero(),
+            em_size: Au::zero(),
+            ascent: Au::zero(),
+            descent: Au::zero(),
+            max_advance: Au::zero(),
+            average_advance: Au::zero(),
+            line_gap: Au::zero(),
             zero_horizontal_advance: None,
             ic_horizontal_advance: None,
+            space_advance: Au::zero(),
         }
     }
 }
@@ -517,6 +522,14 @@ impl FontGroup {
         codepoint: char,
         next_codepoint: Option<char>,
     ) -> Option<FontRef> {
+        // Tab characters are converted into spaces when rendering.
+        // TODO: We should not render a tab character. Instead they should be converted into tab stops
+        // based upon the width of a space character in inline formatting contexts.
+        let codepoint = match codepoint {
+            '\t' => ' ',
+            _ => codepoint,
+        };
+
         let options = FallbackFontSelectionOptions::new(codepoint, next_codepoint);
 
         let should_look_for_small_caps = self.descriptor.variant == font_variant_caps::T::SmallCaps &&
diff --git a/components/fonts/platform/freetype/font.rs b/components/fonts/platform/freetype/font.rs
index 2f0fe23eb80..3a77ab2d8d9 100644
--- a/components/fonts/platform/freetype/font.rs
+++ b/components/fonts/platform/freetype/font.rs
@@ -351,6 +351,10 @@ impl PlatformFontMethods for PlatformFont {
             .glyph_index('\u{6C34}')
             .and_then(|idx| self.glyph_h_advance(idx))
             .map(Au::from_f64_px);
+        let space_advance = self
+            .glyph_index(' ')
+            .and_then(|idx| self.glyph_h_advance(idx))
+            .unwrap_or(average_advance);
 
         FontMetrics {
             underline_size: Au::from_f64_px(underline_size),
@@ -367,6 +371,7 @@ impl PlatformFontMethods for PlatformFont {
             line_gap: Au::from_f64_px(line_height),
             zero_horizontal_advance,
             ic_horizontal_advance,
+            space_advance: Au::from_f64_px(space_advance),
         }
     }
 
diff --git a/components/fonts/platform/macos/font.rs b/components/fonts/platform/macos/font.rs
index 14e3382d5a2..13af8ae034e 100644
--- a/components/fonts/platform/macos/font.rs
+++ b/components/fonts/platform/macos/font.rs
@@ -272,11 +272,17 @@ impl PlatformFontMethods for PlatformFont {
             .glyph_index('0')
             .and_then(|idx| self.glyph_h_advance(idx))
             .map(Au::from_f64_px);
+        let average_advance = zero_horizontal_advance.unwrap_or(max_advance);
+
         let ic_horizontal_advance = self
             .glyph_index('\u{6C34}')
             .and_then(|idx| self.glyph_h_advance(idx))
             .map(Au::from_f64_px);
-        let average_advance = zero_horizontal_advance.unwrap_or(max_advance);
+        let space_advance = self
+            .glyph_index(' ')
+            .and_then(|index| self.glyph_h_advance(index))
+            .map(Au::from_f64_px)
+            .unwrap_or(average_advance);
 
         let metrics = FontMetrics {
             underline_size: Au::from_f64_au(underline_thickness),
@@ -301,6 +307,7 @@ impl PlatformFontMethods for PlatformFont {
             line_gap: Au::from_f64_px(line_gap),
             zero_horizontal_advance,
             ic_horizontal_advance,
+            space_advance,
         };
         debug!(
             "Font metrics (@{} pt): {:?}",
diff --git a/components/fonts/platform/windows/font.rs b/components/fonts/platform/windows/font.rs
index 529ac67c910..e49fa22bbff 100644
--- a/components/fonts/platform/windows/font.rs
+++ b/components/fonts/platform/windows/font.rs
@@ -19,6 +19,7 @@ use log::{debug, warn};
 use style::computed_values::font_stretch::T as StyleFontStretch;
 use style::computed_values::font_weight::T as StyleFontWeight;
 use style::values::computed::font::FontStyle as StyleFontStyle;
+use style::Zero;
 use truetype::tables::WindowsMetrics;
 use truetype::value::Read;
 use webrender_api::FontInstanceFlags;
@@ -242,6 +243,17 @@ impl PlatformFontMethods for PlatformFont {
             .and_then(|idx| self.glyph_h_advance(idx))
             .map(Au::from_f64_px);
 
+        // TODO: These should be retrieved from the OS/2 table if possible and then
+        // fall back to measuring 'x' if that is not available.
+        let average_advance = Au::zero();
+        let max_advance = Au::zero();
+
+        let space_advance = self
+            .glyph_index(' ')
+            .and_then(|index| self.glyph_h_advance(index))
+            .map(Au::from_f64_px)
+            .unwrap_or(average_advance);
+
         let metrics = FontMetrics {
             underline_size: au_from_du(dm.underlineThickness as i32),
             underline_offset: au_from_du_s(dm.underlinePosition as i32),
@@ -252,11 +264,12 @@ impl PlatformFontMethods for PlatformFont {
             em_size: au_from_em(self.em_size as f64),
             ascent: au_from_du_s(dm.ascent as i32),
             descent: au_from_du_s(dm.descent as i32),
-            max_advance: au_from_pt(0.0),     // FIXME
-            average_advance: au_from_pt(0.0), // FIXME
+            max_advance,
+            average_advance,
             line_gap: au_from_du_s((dm.ascent + dm.descent + dm.lineGap as u16) as i32),
             zero_horizontal_advance,
             ic_horizontal_advance,
+            space_advance,
         };
         debug!("Font metrics (@{} pt): {:?}", self.em_size * 12., metrics);
         metrics
diff --git a/components/fonts/shaper.rs b/components/fonts/shaper.rs
index eb8f92b789d..6b61a16183a 100644
--- a/components/fonts/shaper.rs
+++ b/components/fonts/shaper.rs
@@ -545,20 +545,27 @@ impl Shaper {
                 let character = text[byte_range.clone()].chars().next().unwrap();
                 if is_bidi_control(character) {
                     // Don't add any glyphs for bidi control chars
-                } else if character == '\t' {
-                    // Treat tabs in pre-formatted text as a fixed number of spaces.
-                    //
-                    // TODO: Proper tab stops.
-                    const TAB_COLS: i32 = 8;
-                    let (space_glyph_id, space_advance) = glyph_space_advance(self.font);
-                    let advance = Au::from_f64_px(space_advance) * TAB_COLS;
-                    let data =
-                        GlyphData::new(space_glyph_id, advance, Default::default(), true, true);
-                    glyphs.add_glyph_for_byte_index(byte_idx, character, &data);
                 } else {
-                    let shape = glyph_data.entry_for_glyph(glyph_span.start, &mut y_pos);
-                    let advance = self.advance_for_shaped_glyph(shape.advance, character, options);
-                    let data = GlyphData::new(shape.codepoint, advance, shape.offset, true, true);
+                    let (glyph_id, advance, offset) = if character == '\t' {
+                        // Treat tabs in pre-formatted text as a fixed number of spaces. The glyph id does
+                        // not matter here as Servo doesn't render any glyphs for whitespace.
+                        //
+                        // TODO: Proper tab stops. This should happen in layout and be based on the
+                        // size of the space character of the inline formatting context.
+                        let font = unsafe { &(*self.font) };
+                        (
+                            font.glyph_index(' ').unwrap_or(0) as hb_codepoint_t,
+                            font.metrics.space_advance * 8,
+                            Default::default(),
+                        )
+                    } else {
+                        let shape = glyph_data.entry_for_glyph(glyph_span.start, &mut y_pos);
+                        let advance =
+                            self.advance_for_shaped_glyph(shape.advance, character, options);
+                        (shape.codepoint, advance, shape.offset)
+                    };
+
+                    let data = GlyphData::new(glyph_id, advance, offset, true, true);
                     glyphs.add_glyph_for_byte_index(byte_idx, character, &data);
                 }
             } else {
@@ -708,16 +715,6 @@ extern "C" fn glyph_h_advance_func(
     }
 }
 
-fn glyph_space_advance(font: *const Font) -> (hb_codepoint_t, f64) {
-    let space_unicode = ' ';
-    let space_glyph: hb_codepoint_t = match unsafe { (*font).glyph_index(space_unicode) } {
-        Some(g) => g as hb_codepoint_t,
-        None => panic!("No space info"),
-    };
-    let space_advance = unsafe { (*font).glyph_h_advance(space_glyph as GlyphId) };
-    (space_glyph, space_advance)
-}
-
 // Callback to get a font table out of a font.
 extern "C" fn font_table_func(
     _: *mut hb_face_t,
diff --git a/tests/wpt/meta-legacy-layout/css/css-text/tab-size/tab-size-integer-005.html.ini b/tests/wpt/meta-legacy-layout/css/css-text/tab-size/tab-size-integer-005.html.ini
index 50ef08178ba..ce1e35d2ee0 100644
--- a/tests/wpt/meta-legacy-layout/css/css-text/tab-size/tab-size-integer-005.html.ini
+++ b/tests/wpt/meta-legacy-layout/css/css-text/tab-size/tab-size-integer-005.html.ini
@@ -1,2 +1,2 @@
 [tab-size-integer-005.html]
-  expected: CRASH
+  expected: FAIL
diff --git a/tests/wpt/meta/css/css-text/tab-size/tab-size-integer-005.html.ini b/tests/wpt/meta/css/css-text/tab-size/tab-size-integer-005.html.ini
index 50ef08178ba..ce1e35d2ee0 100644
--- a/tests/wpt/meta/css/css-text/tab-size/tab-size-integer-005.html.ini
+++ b/tests/wpt/meta/css/css-text/tab-size/tab-size-integer-005.html.ini
@@ -1,2 +1,2 @@
 [tab-size-integer-005.html]
-  expected: CRASH
+  expected: FAIL