diff --git a/gfx/thebes/gfxFT2Utils.cpp b/gfx/thebes/gfxFT2Utils.cpp
index acc058e73353..28d3e2ffe321 100644
--- a/gfx/thebes/gfxFT2Utils.cpp
+++ b/gfx/thebes/gfxFT2Utils.cpp
@@ -81,7 +81,8 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
 
     gfxFloat emHeight;
     // Scale for vertical design metric conversion: pixels per design unit.
-    gfxFloat yScale;
+    // If this remains at 0.0, we can't use metrics from OS/2 etc.
+    gfxFloat yScale = 0.0;
     if (FT_IS_SCALABLE(mFace)) {
         // Prefer FT_Size_Metrics::x_scale to x_ppem as x_ppem does not
         // have subpixel accuracy.
@@ -93,11 +94,17 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
         yScale = FLOAT_FROM_26_6(FLOAT_FROM_16_16(ftMetrics.y_scale));
         emHeight = mFace->units_per_EM * yScale;
     } else { // Not scalable.
-        // FT_Size_Metrics doc says x_scale is "only relevant for scalable
-        // font formats".
-        gfxFloat emUnit = mFace->units_per_EM;
-        emHeight = ftMetrics.y_ppem;
-        yScale = emHeight / emUnit;
+        // FT_Face doc says units_per_EM and a bunch of following fields
+        // are "only relevant to scalable outlines". If it's an sfnt,
+        // we can get units_per_EM from the 'head' table instead; otherwise,
+        // we don't have a unitsPerEm value so we can't compute/use yScale.
+        const TT_Header* head =
+            static_cast<TT_Header*>(FT_Get_Sfnt_Table(mFace, ft_sfnt_head));
+        if (head) {
+            gfxFloat emUnit = head->Units_Per_EM;
+            emHeight = ftMetrics.y_ppem;
+            yScale = emHeight / emUnit;
+        }
     }
 
     TT_OS2 *os2 =
@@ -108,7 +115,7 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
     aMetrics->maxAdvance = FLOAT_FROM_26_6(ftMetrics.max_advance);
 
     gfxFloat lineHeight;
-    if (os2 && os2->sTypoAscender) {
+    if (os2 && os2->sTypoAscender && yScale > 0.0) {
         aMetrics->emAscent = os2->sTypoAscender * yScale;
         aMetrics->emDescent = -os2->sTypoDescender * yScale;
         FT_Short typoHeight =
@@ -150,7 +157,7 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
         aMetrics->xHeight = -extents.y_bearing;
         aMetrics->aveCharWidth = extents.x_advance;
     } else {
-        if (os2 && os2->sxHeight) {
+        if (os2 && os2->sxHeight && yScale > 0.0) {
             aMetrics->xHeight = os2->sxHeight * yScale;
         } else {
             // CSS 2.1, section 4.3.2 Lengths: "In the cases where it is
@@ -195,7 +202,7 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
     // Therefore get the underline position directly from the table
     // ourselves when this table exists.  Use FreeType's metrics for
     // other (including older PostScript) fonts.
-    if (mFace->underline_position && mFace->underline_thickness) {
+    if (mFace->underline_position && mFace->underline_thickness && yScale > 0.0) {
         aMetrics->underlineSize = mFace->underline_thickness * yScale;
         TT_Postscript *post = static_cast<TT_Postscript*>
             (FT_Get_Sfnt_Table(mFace, ft_sfnt_post));
@@ -211,7 +218,7 @@ gfxFT2LockedFace::GetMetrics(gfxFont::Metrics* aMetrics,
         aMetrics->underlineOffset = -aMetrics->underlineSize;
     }
 
-    if (os2 && os2->yStrikeoutSize && os2->yStrikeoutPosition) {
+    if (os2 && os2->yStrikeoutSize && os2->yStrikeoutPosition && yScale > 0.0) {
         aMetrics->strikeoutSize = os2->yStrikeoutSize * yScale;
         aMetrics->strikeoutOffset = os2->yStrikeoutPosition * yScale;
     } else { // No strikeout info.