diff --git a/gfx/thebes/gfxFT2FontBase.cpp b/gfx/thebes/gfxFT2FontBase.cpp
index e8b53b7a9767..fc76c1ee5522 100644
--- a/gfx/thebes/gfxFT2FontBase.cpp
+++ b/gfx/thebes/gfxFT2FontBase.cpp
@@ -116,7 +116,7 @@ gfxFT2FontBase::GetHorizontalMetrics()
 
     if (MOZ_UNLIKELY(GetStyle()->size <= 0.0)) {
         new(&mMetrics) gfxFont::Metrics(); // zero initialize
-        mSpaceGlyph = 0;
+        mSpaceGlyph = GetGlyph(' ');
     } else {
         gfxFT2LockedFace face(this);
         face.GetMetrics(&mMetrics, &mSpaceGlyph);
@@ -144,8 +144,6 @@ gfxFT2FontBase::GetHorizontalMetrics()
 uint32_t
 gfxFT2FontBase::GetSpaceGlyph()
 {
-    NS_ASSERTION(GetStyle()->size != 0,
-                 "forgot to short-circuit a text run with zero-sized font?");
     GetHorizontalMetrics();
     return mSpaceGlyph;
 }