diff --git a/mozilla/xpcom/ds/nsPersistentProperties.cpp b/mozilla/xpcom/ds/nsPersistentProperties.cpp
index a2e87b9b354..586a2106752 100644
--- a/mozilla/xpcom/ds/nsPersistentProperties.cpp
+++ b/mozilla/xpcom/ds/nsPersistentProperties.cpp
@@ -313,7 +313,7 @@ nsPersistentProperties::GetStringProperty(const nsAString& aKey, nsAString& aVal
     NS_STATIC_CAST(propertyTableEntry*,
                    PL_DHashTableOperate(&mTable, flatKey.get(), PL_DHASH_LOOKUP));
 
-  if (!entry)
+  if (PL_DHASH_ENTRY_IS_FREE(entry))
     return NS_ERROR_FAILURE;
 
   aValue = entry->mValue;