diff --git a/gfx/thebes/src/gfxWindowsFonts.cpp b/gfx/thebes/src/gfxWindowsFonts.cpp
index 5dbb6dbd434..bc405e37428 100644
--- a/gfx/thebes/src/gfxWindowsFonts.cpp
+++ b/gfx/thebes/src/gfxWindowsFonts.cpp
@@ -280,6 +280,14 @@ FontFamily::FindStyleVariations()
     faspd.ff = this;
 
     EnumFontFamiliesExW(hdc, &logFont, (FONTENUMPROCW)FontFamily::FamilyAddStylesProc, (LPARAM)&faspd, 0);
+#ifdef DEBUG
+    if (mVariations.Length() == 0) {
+        char msgBuf[256];
+        (void)sprintf(msgBuf, "no styles available in family \"%s\"",
+                      NS_ConvertUTF16toUTF8(mName).get());
+        NS_ASSERTION(mVariations.Length() != 0, msgBuf);
+    }
+#endif
 
     ReleaseDC(nsnull, hdc);
 
diff --git a/gfx/thebes/src/gfxWindowsPlatform.cpp b/gfx/thebes/src/gfxWindowsPlatform.cpp
index 1546ce0168d..6a120b4adcf 100644
--- a/gfx/thebes/src/gfxWindowsPlatform.cpp
+++ b/gfx/thebes/src/gfxWindowsPlatform.cpp
@@ -191,6 +191,9 @@ gfxWindowsPlatform::HashEnumFunc(nsStringHashKey::KeyType aKey,
     gfxFontStyle style;
     style.langGroup = data->mLangGroup;
     nsRefPtr<FontEntry> aFontEntry = aFontFamily->FindFontEntry(style);
+    NS_ASSERTION(aFontEntry, "couldn't find any font entry in family");
+    if (!aFontEntry)
+        return PL_DHASH_NEXT;
 
 
 #ifndef MOZ_FT2_FONTS
@@ -549,6 +552,10 @@ gfxWindowsPlatform::FindFontForCharProc(nsStringHashKey::KeyType aKey,
     const PRUint32 ch = data->ch;
 
     nsRefPtr<FontEntry> fe = aFontFamily->FindFontEntry(*data->fontToMatch->GetStyle());
+    NS_ASSERTION(fe, "couldn't find any font entry in family");
+    if (!fe)
+        return PL_DHASH_NEXT;
+
     PRInt32 rank = 0;
 
 #ifndef MOZ_FT2_FONTS