diff --git a/sapi/cli/php_cli_server.c b/sapi/cli/php_cli_server.c
index 007718e37b9c..335fc0badffd 100644
--- a/sapi/cli/php_cli_server.c
+++ b/sapi/cli/php_cli_server.c
@@ -175,6 +175,7 @@ typedef struct php_cli_server_client {
 	php_http_parser parser;
 	bool request_read;
 	bool too_large_post;
+	bool expect_continue;
 	zend_string *current_header_name;
 	zend_string *current_header_value;
 	enum { HEADER_NONE=0, HEADER_FIELD, HEADER_VALUE } last_header_element;
@@ -1791,6 +1792,12 @@ static int php_cli_server_client_read_request_on_headers_complete(php_http_parse
 		return 2;
 	}
 
+	zval *expect_val = zend_hash_str_find(&client->request.headers, "expect", sizeof("expect") - 1);
+	if (expect_val && Z_TYPE_P(expect_val) == IS_STRING
+			&& zend_string_equals_literal_ci(Z_STR_P(expect_val), "100-continue")) {
+		client->expect_continue = true;
+	}
+
 	return 0;
 }
 
@@ -1886,6 +1893,26 @@ static int php_cli_server_client_read_request(php_cli_server_client *client, cha
 	}
 	client->parser.data = client;
 	nbytes_consumed = php_http_parser_execute(&client->parser, &settings, buf, nbytes_read);
+	if (client->expect_continue && !client->request_read) {
+		/* Parser completed headers with Expect: 100-continue but hasn't
+		 * finished reading the body. Send 100 Continue before the client
+		 * sends the request body. */
+		smart_str buffer = { 0 };
+		bool send_failed = true;
+		append_http_status_line(&buffer, client->parser.http_major * 100 + client->parser.http_minor, 100, 0);
+		smart_str_appendl(&buffer, "\r\n", 2);
+		smart_str_0(&buffer);
+		zend_try {
+			php_cli_server_client_send_through(client, ZSTR_VAL(buffer.s), ZSTR_LEN(buffer.s));
+			send_failed = false;
+		} zend_end_try();
+		smart_str_free(&buffer);
+		client->expect_continue = false;
+		if (send_failed) {
+			*errstr = php_socket_strerror(php_socket_errno(), NULL, 0);
+			return -1;
+		}
+	}
 	if (nbytes_consumed != (size_t)nbytes_read && !client->too_large_post) {
 		if (php_cli_server_log_level >= PHP_CLI_SERVER_LOG_ERROR) {
 			if ((buf[0] & 0x80) /* SSLv2 */ || buf[0] == 0x16 /* SSLv3/TLSv1 */) {
@@ -1981,6 +2008,7 @@ static void php_cli_server_client_ctor(php_cli_server_client *client, php_cli_se
 	php_http_parser_init(&client->parser, PHP_HTTP_REQUEST);
 	client->request_read = false;
 	client->too_large_post = false;
+	client->expect_continue = false;
 
 	client->last_header_element = HEADER_NONE;
 	client->current_header_name = NULL;
diff --git a/sapi/cli/tests/php_cli_server_expect_100_continue_curl.phpt b/sapi/cli/tests/php_cli_server_expect_100_continue_curl.phpt
new file mode 100644
index 000000000000..37886fc25e1e
--- /dev/null
+++ b/sapi/cli/tests/php_cli_server_expect_100_continue_curl.phpt
@@ -0,0 +1,35 @@
+--TEST--
+Expect 100-continue behavior in PHP development server (curl)
+--SKIPIF--
+<?php
+include "skipif.inc";
+?>
+--EXTENSIONS--
+curl
+--FILE--
+<?php
+include 'php_cli_server.inc';
+$server = php_cli_server_start();
+
+// Generate a POST body larger than 1MB to trigger Expect: 100-continue
+$body = str_repeat('A', 1024 * 1024 + 1);
+
+$ch = curl_init();
+curl_setopt($ch, CURLOPT_URL, PHP_CLI_SERVER_ADDRESS);
+curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
+curl_setopt($ch, CURLOPT_POSTFIELDS, $body);
+
+// Set a high timeout for 100-continue response
+curl_setopt($ch, CURLOPT_EXPECT_100_TIMEOUT_MS, 2000);
+
+curl_exec($ch);
+var_dump(curl_errno($ch));
+
+echo "Did the PHP development server send a HTTP/1.1 100 Continue header?\n";
+$start_transfer_time = curl_getinfo($ch, CURLINFO_STARTTRANSFER_TIME_T);
+var_dump($start_transfer_time < 1_000_000);
+?>
+--EXPECT--
+int(0)
+Did the PHP development server send a HTTP/1.1 100 Continue header?
+bool(true)
diff --git a/sapi/cli/tests/php_cli_server_expect_100_continue_socket.phpt b/sapi/cli/tests/php_cli_server_expect_100_continue_socket.phpt
new file mode 100644
index 000000000000..ddd7d50d28f7
--- /dev/null
+++ b/sapi/cli/tests/php_cli_server_expect_100_continue_socket.phpt
@@ -0,0 +1,74 @@
+--TEST--
+Expect 100-continue behavior in PHP development server (sockets)
+--SKIPIF--
+<?php
+include "skipif.inc";
+?>
+--FILE--
+<?php
+include "php_cli_server.inc";
+php_cli_server_start();
+
+echo "# Send Expect: 100-continue header, receive 100 Continue response.\n";
+$fp = php_cli_server_connect();
+fwrite($fp, "POST / HTTP/1.1\r\nExpect: 100-continue\r\nContent-Length: 4\r\nConnection: close\r\n\r\n");
+echo fgets($fp);
+echo fgets($fp);
+fwrite($fp, "body");
+echo fgets($fp);
+fclose($fp);
+
+echo "# Send Expect: 100-continue header and disconnect.\n";
+$fp = php_cli_server_connect();
+if (extension_loaded('sockets')) {
+    // Set SO_LINGER timeout to zero so that send fails on the server immediately
+    socket_set_option(
+        socket_import_stream($fp),
+        SOL_SOCKET,
+        SO_LINGER,
+        [
+            'l_onoff' => 1,
+            'l_linger' => 0,
+        ]
+    );
+}
+stream_socket_shutdown($fp, STREAM_SHUT_RD);
+fwrite($fp, "POST / HTTP/1.1\r\nExpect: 100-continue\r\nContent-Length: 4\r\nConnection: close\r\n\r\n");
+fclose($fp);
+
+$fp = php_cli_server_connect();
+fwrite($fp, "GET / HTTP/1.1\r\nConnection: close\r\n\r\n");
+echo fgets($fp);
+fclose($fp);
+
+echo "# GET with Expect header (no body).\n";
+$fp = php_cli_server_connect();
+fwrite($fp, "GET / HTTP/1.1\r\nExpect: 100-continue\r\nConnection: close\r\n\r\n");
+echo fgets($fp);
+fclose($fp);
+
+echo "# POST with empty body.\n";
+$fp = php_cli_server_connect();
+fwrite($fp, "POST / HTTP/1.1\r\nExpect: 100-continue\r\nContent-Length: 0\r\nConnection: close\r\n\r\n");
+echo fgets($fp);
+fclose($fp);
+
+echo "# Lower-case expect header.\n";
+$fp = php_cli_server_connect();
+fwrite($fp, "POST / HTTP/1.1\r\nexpect: 100-continue\r\nContent-Length: 4\r\nConnection: close\r\n\r\n");
+echo fgets($fp);
+fclose($fp);
+?>
+--EXPECT--
+# Send Expect: 100-continue header, receive 100 Continue response.
+HTTP/1.1 100 Continue
+
+HTTP/1.1 200 OK
+# Send Expect: 100-continue header and disconnect.
+HTTP/1.1 200 OK
+# GET with Expect header (no body).
+HTTP/1.1 200 OK
+# POST with empty body.
+HTTP/1.1 200 OK
+# Lower-case expect header.
+HTTP/1.1 100 Continue