diff --git a/gfx/thebes/gfxFontEntry.cpp b/gfx/thebes/gfxFontEntry.cpp
index e8bb39e689..e07415983a 100644
--- a/gfx/thebes/gfxFontEntry.cpp
+++ b/gfx/thebes/gfxFontEntry.cpp
@@ -592,7 +592,8 @@ gfxFontEntry::ShareFontTableAndGetBlob(uint32_t aTag,
     }
 
     FontTableHashEntry *entry = mFontTableCache->PutEntry(aTag);
-    if (MOZ_UNLIKELY(!entry)) { // OOM
+    if (MOZ_UNLIKELY(!entry)) { 
+        // OOM or other issue storing the entry. 
         return nullptr;
     }
 
diff --git a/gfx/thebes/gfxFontEntry.h b/gfx/thebes/gfxFontEntry.h
index 162fe4f083..506c240270 100644
--- a/gfx/thebes/gfxFontEntry.h
+++ b/gfx/thebes/gfxFontEntry.h
@@ -265,7 +265,8 @@ public:
     // unregisters the table from the font entry.
     //
     // Pass nullptr for aBuffer to indicate that the table is not present and
-    // nullptr will be returned.  Also returns nullptr on OOM.
+    // nullptr will be returned.  Also returns nullptr on OOM or when there are
+    // other issues storing the entry in the cache table.
     hb_blob_t *ShareFontTableAndGetBlob(uint32_t aTag,
                                         nsTArray<uint8_t>* aTable);