https://bugs.gentoo.org/840526
--- a/src/modules/rtp_rtcp/source/rtp_packetizer_av1_test_helper.cc
+++ b/src/modules/rtp_rtcp/source/rtp_packetizer_av1_test_helper.cc
@@ -10,6 +10,7 @@
 
 #include "modules/rtp_rtcp/source/rtp_packetizer_av1_test_helper.h"
 
+#include <cstddef>
 #include <stdint.h>
 
 #include <initializer_list>
@@ -42,7 +43,7 @@ std::vector<uint8_t> BuildAv1Frame(std::initializer_list<Av1Obu> obus) {
     }
     if (obu.header_ & kAv1ObuSizePresentBit) {
       // write size in leb128 format.
-      size_t payload_size = obu.payload_.size();
+      std::size_t payload_size = obu.payload_.size();
       while (payload_size >= 0x80) {
         raw.push_back(0x80 | (payload_size & 0x7F));
         payload_size >>= 7;