--- a/netwerk/dns/nsHostResolver.cpp
+++ b/netwerk/dns/nsHostResolver.cpp
@@ -471,16 +471,17 @@ nsHostRecord::GetPriority(uint16_t aFlag
 
 // Returns true if the entry can be removed, or false if it should be left.
 // Sets mResolveAgain true for entries being resolved right now.
 bool
 nsHostRecord::RemoveOrRefresh()
 {
     // no need to flush TRRed names, they're not resolved "locally"
     Cancel();
+    MutexAutoLock lock(addr_info_lock);
     if (addr_info && addr_info->IsTRR()) {
         return false;
     }
     if (mNative) {
         if (!onQueue) {
             // The request has been passed to the OS resolver. The resultant DNS
             // record should be considered stale and not trusted; set a flag to
             // ensure it is called again.