diff --git a/metrics_prometheus.go b/metrics_prometheus.go
index 841ff1d9..7ffc94fe 100644
--- a/metrics_prometheus.go
+++ b/metrics_prometheus.go
@@ -75,7 +75,7 @@ func (p *metricsPrometheusOutputHandler) flushMetric(
 	})
 
 	if buf.Len() == 0 {
-		logCtx.Debug("metrics export (no metrics in msg): keys [%v]", tags)
+		logCtx.Debug(fmt.Sprintf("metrics export (no metrics in msg): keys [%v]", tags))
 		return
 	}
 
diff --git a/xport_grpc_test.go b/xport_grpc_test.go
index cbfeaa5a..f35b8273 100644
--- a/xport_grpc_test.go
+++ b/xport_grpc_test.go
@@ -112,7 +112,7 @@ func TestGRPCRun(t *testing.T) {
 	}
 	log.Debug("       END       ==============================================")
 
-	log.Debug("GRPCTEST: exited datachannel after %d events\n", i)
+	log.Debug(fmt.Sprintf("GRPCTEST: exited datachannel after %d events\n", i))
 	respChan := make(chan *ctrlMsg)
 	request := &ctrlMsg{
 		id:       SHUTDOWN,