--- a/netwerk/dns/nsHostResolver.cpp
+++ b/netwerk/dns/nsHostResolver.cpp
@@ -289,17 +289,18 @@ nsHostRecord::ResolveComplete()
         } else {
             AccumulateCategorical(((mTrrDuration - mNativeDuration) > k50ms) ?
                                   Telemetry::LABELS_DNS_TRR_RACE::NativeFasterBy50 :
                                   Telemetry::LABELS_DNS_TRR_RACE::NativeFaster);
             LOG(("nsHostRecord::Complete %s Dns Race: NATIVE\n", host.get()));
         }
     }
 
-    if (mTRRUsed && mNativeUsed) {
+    if (mTRRUsed && mNativeUsed &&
+        ((mResolverMode == MODE_SHADOW) || (mResolverMode == MODE_PARALLEL))) {
         // both were used, accumulate comparative success
         AccumulateCategorical(mNativeSuccess && mTRRSuccess?
                               Telemetry::LABELS_DNS_TRR_COMPARE::BothWorked :
                               ((mNativeSuccess ? Telemetry::LABELS_DNS_TRR_COMPARE::NativeWorked :
                                 (mTRRSuccess ? Telemetry::LABELS_DNS_TRR_COMPARE::TRRWorked:
                                  Telemetry::LABELS_DNS_TRR_COMPARE::BothFailed))));
     }