diff --git a/zapgrpc/zapgrpc.go b/zapgrpc/zapgrpc.go
index 0381622a6..24b673849 100644
--- a/zapgrpc/zapgrpc.go
+++ b/zapgrpc/zapgrpc.go
@@ -39,6 +39,7 @@ func (f optionFunc) apply(log *Logger) {
 
 // WithDebug configures a Logger to print at zap's DebugLevel instead of
 // InfoLevel.
+// It only affects the Printf, Println and Print methods, which are only used in the gRPC v1 grpclog.Logger API.
 // Deprecated: use grpclog.SetLoggerV2() for v2 API.
 func WithDebug() Option {
 	return optionFunc(func(logger *Logger) {