diff --git a/ci/build_picotls.ps1 b/ci/build_picotls.ps1
index 15d269a359065ea15ad3cec2486a6612109e9167..7299ebecf8446bd48ade9b0109a20c58b1292f01 100644
--- a/ci/build_picotls.ps1
+++ b/ci/build_picotls.ps1
@@ -1,5 +1,5 @@
 # Build at a known-good commit
-$COMMIT_ID="241f684346d3be4f5ba8dc46010e9f9486a79991"
+$COMMIT_ID="9cab5f9fd82040fcbf6a4cb0ac276dec6c6aa48f"
 
 # Match expectations of picotlsvs project.
 foreach ($dir in "$Env:OPENSSLDIR","$Env:OPENSSL64DIR") {
diff --git a/ci/build_picotls.sh b/ci/build_picotls.sh
index ca4b51daa57ef2e98899957714fec47f65724504..53d08a57c0809257b0f2b72427ded1fc31b309b6 100755
--- a/ci/build_picotls.sh
+++ b/ci/build_picotls.sh
@@ -2,7 +2,7 @@
 #build last picotls master (for Travis)
 
 # Build at a known-good commit
-COMMIT_ID=241f684346d3be4f5ba8dc46010e9f9486a79991
+COMMIT_ID=9cab5f9fd82040fcbf6a4cb0ac276dec6c6aa48f
 
 cd ..
 git clone --branch master --single-branch --shallow-submodules --recurse-submodules --no-tags https://github.com/h2o/picotls
diff --git a/picoquic/tls_api.c b/picoquic/tls_api.c
index f69afb45c417f8a2ad31cc102130bdba27b3f7a9..d5703f4e2632d58b4d6f480d7a9c6df92bc7769f 100644
--- a/picoquic/tls_api.c
+++ b/picoquic/tls_api.c
@@ -1035,7 +1035,7 @@ int picoquic_master_tlscontext(picoquic_quic_t* quic,
 
         ctx->send_change_cipher_spec = 0;
 
-        ctx->hkdf_label_prefix = PICOQUIC_LABEL_QUIC_BASE;
+        ctx->hkdf_label_prefix__obsolete = PICOQUIC_LABEL_QUIC_BASE;
         ctx->update_traffic_key = picoquic_set_update_traffic_key_callback();
 
         if (quic->p_simulated_time == NULL) {