diff --git a/netwerk/cookie/nsCookieService.cpp b/netwerk/cookie/nsCookieService.cpp
index e78b50d527..74683e7a49 100644
--- a/netwerk/cookie/nsCookieService.cpp
+++ b/netwerk/cookie/nsCookieService.cpp
@@ -49,6 +49,7 @@
 #include "mozilla/storage.h"
 #include "mozilla/AutoRestore.h"
 #include "mozilla/FileUtils.h"
+#include "mozilla/ScopeExit.h"
 #include "nsIConsoleService.h"
 #include "nsVariant.h"
 
@@ -845,6 +846,10 @@ nsCookieService::TryInitDB(bool aRecreateDB)
     getter_AddRefs(mDefaultDBState->syncConn));
   NS_ENSURE_SUCCESS(rv, RESULT_RETRY);
 
+  auto guard = MakeScopeExit([&] {
+    mDefaultDBState->syncConn = nullptr;
+  });
+
   bool tableExists = false;
   mDefaultDBState->syncConn->TableExists(NS_LITERAL_CSTRING("moz_cookies"),
     &tableExists);
@@ -1596,8 +1601,8 @@ nsCookieService::CleanupDefaultDBConnection()
   // Null out the database connections. If 'dbConn' has not been used for any
   // asynchronous operations yet, this will synchronously close it; otherwise,
   // it's expected that the caller has performed an AsyncClose prior.
+  // Note 'syncConn' is auto-closed on scope exit.
   mDefaultDBState->dbConn = nullptr;
-  mDefaultDBState->syncConn = nullptr;
 
   // Manually null out our listeners. This is necessary because they hold a
   // strong ref to the DBState itself. They'll stay alive until whatever
@@ -2619,7 +2624,7 @@ nsCookieService::Read()
     tuple->cookie = GetCookieFromRow(stmt, attrs);
   }
 
-  mDefaultDBState->syncConn = nullptr;
+  // Note: 'syncConn' is auto-closed on scope exit.
   
   COOKIE_LOGSTRING(LogLevel::Debug, ("Read(): %zu cookies read", mReadArray.Length()));