diff --git a/src/servo-gfx/font.rs b/src/servo-gfx/font.rs
index 1b0b6970782..d04f065b8a9 100644
--- a/src/servo-gfx/font.rs
+++ b/src/servo-gfx/font.rs
@@ -375,6 +375,8 @@ pub trait FontMethods {
                               range: &Range,
                               baseline_origin: Point2D<Au>,
                               color: Color);
+    // This calculates run metrics for the specified character range
+    // within the provided textrun.
     fn measure_text(&TextRun, &const Range) -> RunMetrics;
     fn shape_text(@self, &str, &mut GlyphStore);
     fn get_descriptor() -> FontDescriptor;
@@ -448,12 +450,10 @@ pub impl Font : FontMethods {
     }
 
     fn measure_text(run: &TextRun, range: &const Range) -> RunMetrics {
-        assert range.is_valid_for_string(run.text);
-
         // TODO(Issue #199): alter advance direction for RTL
         // TODO(Issue #98): using inter-char and inter-word spacing settings  when measuring text
         let mut advance = Au(0);
-        for run.glyphs.iter_glyphs_for_byte_range(range) |_i, glyph| {
+        for run.glyphs.iter_glyphs_for_char_range(range) |_i, glyph| {
             advance += glyph.advance();
         }
         let mut bounds = Rect(Point2D(Au(0), -self.metrics.ascent),
diff --git a/src/servo-gfx/text/glyph.rs b/src/servo-gfx/text/glyph.rs
index 5cd17125294..91011d78774 100644
--- a/src/servo-gfx/text/glyph.rs
+++ b/src/servo-gfx/text/glyph.rs
@@ -604,6 +604,7 @@ impl GlyphStore {
     }
 
     pure fn iter_glyphs_for_byte_range(range: &const Range, cb: fn&(uint, GlyphInfo/&) -> bool) {
+        warn!("Using deprecated iter_glyphs_for_byte_range API!");
         if range.begin() >= self.entry_buffer.len() {
             error!("iter_glyphs_for_range: range.begin beyond length!");
             return;
@@ -613,9 +614,11 @@ impl GlyphStore {
             return;
         }
 
-        // TODO: actually compute char indexes from byte indexes.
-        let char_range = copy *range;
-        for char_range.eachi |i| {
+        self.iter_glyphs_for_char_range(range, cb)
+    }
+
+    pure fn iter_glyphs_for_char_range(range: &const Range, cb: fn&(uint, GlyphInfo/&) -> bool) {
+        for range.eachi |i| {
 	    if !self.iter_glyphs_for_char_index(i, cb) { break; }
 	}
     }
diff --git a/src/servo-gfx/text/text_run.rs b/src/servo-gfx/text/text_run.rs
index deaa5377f44..550802f084b 100644
--- a/src/servo-gfx/text/text_run.rs
+++ b/src/servo-gfx/text/text_run.rs
@@ -1,6 +1,9 @@
 use font_context::FontContext;
 use geometry::Au;
-use glyph::GlyphStore;
+use glyph::{
+    BreakTypeNormal,
+    GlyphStore,
+};
 use servo_gfx_font::{Font, FontDescriptor, RunMetrics};
 use servo_gfx_util::range::Range;
 
@@ -42,6 +45,7 @@ impl SendableTextRun {
 impl TextRun {
     static fn new(font: @Font, text: ~str) -> TextRun {
         let mut glyph_store = GlyphStore::new(str::char_len(text));
+        TextRun::compute_potential_breaks(text, &mut glyph_store);
         font.shape_text(text, &mut glyph_store);
 
         let run = TextRun {
@@ -52,6 +56,44 @@ impl TextRun {
         return move run;
     }
 
+    static fn compute_potential_breaks(text: &str, glyphs: &mut GlyphStore) {
+        // TODO(Issue #230): do a better job. See Gecko's LineBreaker.
+
+        let mut i = 0u;
+        let mut prev_is_whitespace = false;
+        while i < text.len() {
+            let {ch, next} = str::char_range_at(text, i);
+            // set char properties.
+            match ch {
+                ' '  => { glyphs.set_char_is_space(i); },
+                '\t' => { glyphs.set_char_is_tab(i); },
+                '\n' => { glyphs.set_char_is_newline(i); },
+                _ => {}
+            }
+
+            // set line break opportunities at whitespace/non-whitespace boundaries.
+            if prev_is_whitespace {
+                match ch {
+                    ' ' | '\t' | '\n' => {},
+                    _ => {
+                        glyphs.set_can_break_before(i, BreakTypeNormal);
+                        prev_is_whitespace = false;
+                    }
+                }
+            } else {
+                match ch {
+                    ' ' | '\t' | '\n' => {
+                        glyphs.set_can_break_before(i, BreakTypeNormal);
+                        prev_is_whitespace = true;
+                    },
+                    _ => { }
+                }
+            }
+
+            i = next;
+        }
+    }
+
     pub fn serialize(&self) -> SendableTextRun {
         SendableTextRun {
             text: copy self.text,