diff --git a/deployment/terraform/modules/osv/osv_api.tf b/deployment/terraform/modules/osv/osv_api.tf
index 7a55604a1fb..d85c8c80a93 100644
--- a/deployment/terraform/modules/osv/osv_api.tf
+++ b/deployment/terraform/modules/osv/osv_api.tf
@@ -126,7 +126,7 @@ resource "google_cloud_run_service" "api" {
         image = data.google_container_registry_image.api.image_url
         env {
           name  = "ESPv2_ARGS"
-          value = "^++^--transcoding_preserve_proto_field_names++--envoy_connection_buffer_limit_bytes=104857600"
+          value = "^++^--transcoding_preserve_proto_field_names++--envoy_connection_buffer_limit_bytes=104857600++--underscores_in_headers"
         }
         resources {
           limits = {
diff --git a/gcp/api/test_server.py b/gcp/api/test_server.py
index 01a6196e417..6076210c83c 100644
--- a/gcp/api/test_server.py
+++ b/gcp/api/test_server.py
@@ -106,6 +106,7 @@ def start_esp(port, backend_port, credential_path, log_path):
         '--disable_tracing',
         '--service=api-test.osv.dev',
         '--rollout_strategy=managed',
+        '--underscores_in_headers',
         f'--listener_port={port}',
         f'--backend=grpc://{host}:{backend_port}',
         '--enable_debug',
@@ -134,6 +135,7 @@ def start_esp(port, backend_port, credential_path, log_path):
         '--disable_tracing',
         '--service=api-test.osv.dev',
         '--rollout_strategy=managed',
+        '--underscores_in_headers',
         f'--listener_port={port}',
         f'--backend=grpc://{host}:{backend_port}',
         f'--service_account_key=/esp/{credential_name}',