diff --git a/gennghttpxfun.py b/gennghttpxfun.py
index 2f72cb06..ab9e7e44 100755
--- a/gennghttpxfun.py
+++ b/gennghttpxfun.py
@@ -132,6 +132,7 @@ OPTIONS = [
     "no-kqueue",
     "frontend-http2-settings-timeout",
     "backend-http2-settings-timeout",
+    "api-max-request-body",
 ]
 
 LOGVARS = [
diff --git a/src/shrpx.cc b/src/shrpx.cc
index fcc45638..044e272b 100644
--- a/src/shrpx.cc
+++ b/src/shrpx.cc
@@ -1183,6 +1183,9 @@ void fill_default_config() {
     downstreamconf.response_buffer_size = 128_k;
     downstreamconf.family = AF_UNSPEC;
   }
+
+  auto &apiconf = mod_config()->api;
+  apiconf.max_request_body = 16_k;
 }
 
 } // namespace
@@ -1914,6 +1917,12 @@ HTTP:
               HTTP  status  code.  If  error  status  code comes  from
               backend server, the custom error pages are not used.
 
+API:
+  --api-max-request-body=<SIZE>
+              Set the maximum size of request body for API request.
+              Default: )" << util::utos_unit(get_config()->api.max_request_body)
+      << R"(
+
 Debug:
   --frontend-http2-dump-request-header=<PATH>
               Dumps request headers received by HTTP/2 frontend to the
@@ -2447,6 +2456,7 @@ int main(int argc, char **argv) {
          &flag, 124},
         {SHRPX_OPT_BACKEND_HTTP2_SETTINGS_TIMEOUT.c_str(), required_argument,
          &flag, 125},
+        {SHRPX_OPT_API_MAX_REQUEST_BODY.c_str(), required_argument, &flag, 126},
         {nullptr, 0, nullptr, 0}};
 
     int option_index = 0;
@@ -3036,6 +3046,10 @@ int main(int argc, char **argv) {
         cmdcfgs.emplace_back(SHRPX_OPT_BACKEND_HTTP2_SETTINGS_TIMEOUT,
                              StringRef{optarg});
         break;
+      case 126:
+        // --api-max-request-body
+        cmdcfgs.emplace_back(SHRPX_OPT_API_MAX_REQUEST_BODY, StringRef{optarg});
+        break;
       default:
         break;
       }
diff --git a/src/shrpx_api_downstream_connection.cc b/src/shrpx_api_downstream_connection.cc
index 2501d9da..fb4867a8 100644
--- a/src/shrpx_api_downstream_connection.cc
+++ b/src/shrpx_api_downstream_connection.cc
@@ -87,6 +87,15 @@ int APIDownstreamConnection::push_request_headers() {
     return 0;
   }
 
+  // This works with req.fs.content_length == -1
+  if (req.fs.content_length >
+      static_cast<int64_t>(get_config()->api.max_request_body)) {
+    send_reply(
+        413, http2::get_status_string(downstream_->get_block_allocator(), 413));
+
+    return 0;
+  }
+
   return 0;
 }
 
@@ -98,7 +107,15 @@ int APIDownstreamConnection::push_upload_data_chunk(const uint8_t *data,
 
   auto output = downstream_->get_request_buf();
 
-  // TODO limit the maximum payload size
+  auto &apiconf = get_config()->api;
+
+  if (output->rleft() + datalen > apiconf.max_request_body) {
+    send_reply(
+        413, http2::get_status_string(downstream_->get_block_allocator(), 413));
+
+    return 0;
+  }
+
   output->append(data, datalen);
 
   // We don't have to call Upstream::resume_read() here, because
@@ -116,7 +133,7 @@ int APIDownstreamConnection::end_upload_data() {
   auto output = downstream_->get_request_buf();
 
   struct iovec iov;
-  auto iovcnt = output->riovec(&iov, 1);
+  auto iovcnt = output->riovec(&iov, 2);
 
   constexpr auto body = StringRef::from_lit("200 OK");
   constexpr auto error_body = StringRef::from_lit("400 Bad Request");
@@ -127,6 +144,19 @@ int APIDownstreamConnection::end_upload_data() {
     return 0;
   }
 
+  std::unique_ptr<uint8_t[]> large_buf;
+
+  // If data spans in multiple chunks, pull them up into one
+  // contiguous buffer.
+  if (iovcnt > 1) {
+    large_buf = make_unique<uint8_t[]>(output->rleft());
+    auto len = output->rleft();
+    output->remove(large_buf.get(), len);
+
+    iov.iov_base = large_buf.get();
+    iov.iov_len = len;
+  }
+
   Config config{};
   config.conn.downstream = std::make_shared<DownstreamConfig>();
   const auto &downstreamconf = config.conn.downstream;
diff --git a/src/shrpx_config.cc b/src/shrpx_config.cc
index 5586e934..92d63e21 100644
--- a/src/shrpx_config.cc
+++ b/src/shrpx_config.cc
@@ -915,6 +915,7 @@ enum {
   SHRPX_OPTID_ADD_RESPONSE_HEADER,
   SHRPX_OPTID_ADD_X_FORWARDED_FOR,
   SHRPX_OPTID_ALTSVC,
+  SHRPX_OPTID_API_MAX_REQUEST_BODY,
   SHRPX_OPTID_BACKEND,
   SHRPX_OPTID_BACKEND_ADDRESS_FAMILY,
   SHRPX_OPTID_BACKEND_CONNECTIONS_PER_FRONTEND,
@@ -1429,6 +1430,11 @@ int option_lookup_token(const char *name, size_t namelen) {
         return SHRPX_OPTID_VERIFY_CLIENT_CACERT;
       }
       break;
+    case 'y':
+      if (util::strieq_l("api-max-request-bod", name, 19)) {
+        return SHRPX_OPTID_API_MAX_REQUEST_BODY;
+      }
+      break;
     }
     break;
   case 21:
@@ -2712,6 +2718,8 @@ int parse_config(Config *config, const StringRef &opt, const StringRef &optarg,
   case SHRPX_OPTID_BACKEND_HTTP2_SETTINGS_TIMEOUT:
     return parse_duration(&config->http2.downstream.timeout.settings, opt,
                           optarg);
+  case SHRPX_OPTID_API_MAX_REQUEST_BODY:
+    return parse_uint_with_unit(&config->api.max_request_body, opt, optarg);
   case SHRPX_OPTID_CONF:
     LOG(WARN) << "conf: ignored";
 
diff --git a/src/shrpx_config.h b/src/shrpx_config.h
index c1d71c8c..40b626fd 100644
--- a/src/shrpx_config.h
+++ b/src/shrpx_config.h
@@ -280,6 +280,8 @@ constexpr auto SHRPX_OPT_FRONTEND_HTTP2_SETTINGS_TIMEOUT =
     StringRef::from_lit("frontend-http2-settings-timeout");
 constexpr auto SHRPX_OPT_BACKEND_HTTP2_SETTINGS_TIMEOUT =
     StringRef::from_lit("backend-http2-settings-timeout");
+constexpr auto SHRPX_OPT_API_MAX_REQUEST_BODY =
+    StringRef::from_lit("api-max-request-body");
 
 constexpr size_t SHRPX_OBFUSCATED_NODE_LENGTH = 8;
 
@@ -649,6 +651,11 @@ struct ConnectionConfig {
   std::shared_ptr<DownstreamConfig> downstream;
 };
 
+struct APIConfig {
+  // Maximum request body size for one API request
+  size_t max_request_body;
+};
+
 struct Config {
   HttpProxy downstream_http_proxy;
   HttpConfig http;
@@ -656,6 +663,7 @@ struct Config {
   TLSConfig tls;
   LoggingConfig logging;
   ConnectionConfig conn;
+  APIConfig api;
   ImmutableString pid_file;
   ImmutableString conf_path;
   ImmutableString user;