diff --git a/library/Requests/Transport/cURL.php b/library/Requests/Transport/cURL.php
index 2453de1db..01bcf3b71 100644
--- a/library/Requests/Transport/cURL.php
+++ b/library/Requests/Transport/cURL.php
@@ -317,6 +317,21 @@ protected function setup_handle($url, $headers, $data, $options) {
 			$headers['Connection'] = 'close';
 		}
 
+		/**
+		 * Add "Expect" header.
+		 *
+		 * By default, cURL adds a "Expect: 100-Continue" to most requests. This header can
+		 * add as much as a second to the time it takes for cURL to perform a request. To
+		 * prevent this, we need to set an empty "Expect" header. To match the behaviour of
+		 * Guzzle, we'll add the empty header to requests that are smaller than 1 MB and use
+		 * HTTP/1.1.
+		 *
+		 * https://curl.se/mail/lib-2017-07/0013.html
+		 */
+		if (!isset($headers['Expect']) && $options['protocol_version'] === 1.1) {
+			$headers['Expect'] = $this->get_expect_header($data);
+		}
+
 		$headers = Requests::flatten($headers);
 
 		if (!empty($data)) {
@@ -546,4 +561,29 @@ public static function test($capabilities = array()) {
 
 		return true;
 	}
+
+	/**
+	 * Get the correct "Expect" header for the given request data.
+	 *
+	 * @param string|array $data Data to send either as the POST body, or as parameters in the URL for a GET/HEAD.
+	 * @return string The "Expect" header.
+	 */
+	protected function get_expect_header($data) {
+		if (!is_array($data)) {
+			return strlen((string) $data) >= 1048576 ? '100-Continue' : '';
+		}
+
+		$bytesize = 0;
+		$iterator = new RecursiveIteratorIterator(new RecursiveArrayIterator($data));
+
+		foreach ($iterator as $datum) {
+			$bytesize += strlen((string) $datum);
+
+			if ($bytesize >= 1048576) {
+				return '100-Continue';
+			}
+		}
+
+		return '';
+	}
 }
diff --git a/tests/Transport/cURL.php b/tests/Transport/cURL.php
index d0095228c..0690d7b4b 100644
--- a/tests/Transport/cURL.php
+++ b/tests/Transport/cURL.php
@@ -36,4 +36,104 @@ public function testRevokedHTTPS() {
 	public function testBadDomain() {
 		parent::testBadDomain();
 	}
+
+	/**
+	 * @small
+	 */
+	public function testDoesntOverwriteExpectHeaderIfManuallySet() {
+		$headers = array(
+			'Expect' => 'foo',
+		);
+		$request = Requests::post(httpbin('/post'), $headers, array(), $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertSame($headers['Expect'], $result['headers']['Expect']);
+	}
+
+	/**
+	 * @small
+	 */
+	public function testDoesntSetExpectHeaderIfBodyExactly1MbButProtocolIsnt11() {
+		$options = array(
+			'protocol_version' => 1.0,
+		);
+		$request = Requests::post(httpbin('/post'), array(), str_repeat('x', 1048576), $this->getOptions($options));
+
+		$result = json_decode($request->body, true);
+
+		$this->assertFalse(isset($result['headers']['Expect']));
+	}
+
+	/**
+	 * @small
+	 */
+	public function testSetsEmptyExpectHeaderWithDefaultSettings() {
+		$request = Requests::post(httpbin('/post'), array(), array(), $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertFalse(isset($result['headers']['Expect']));
+	}
+
+	/**
+	 * @small
+	 */
+	public function testSetsEmptyExpectHeaderIfBodyIsANestedArrayLessThan1Mb() {
+		$data    = array(
+			str_repeat('x', 148576),
+			array(
+				str_repeat('x', 548576),
+			),
+		);
+		$request = Requests::post(httpbin('/post'), array(), $data, $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertFalse(isset($result['headers']['Expect']));
+	}
+
+	public function testSetsExpectHeaderIfBodyIsExactlyA1MbString() {
+		$request = Requests::post(httpbin('/post'), array(), str_repeat('x', 1048576), $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertSame('100-Continue', $result['headers']['Expect']);
+	}
+
+	public function testSetsExpectHeaderIfBodyIsANestedArrayGreaterThan1Mb() {
+		$data    = array(
+			str_repeat('x', 148576),
+			array(
+				str_repeat('x', 548576),
+				array(
+					str_repeat('x', 648576),
+				),
+			),
+		);
+		$request = Requests::post(httpbin('/post'), array(), $data, $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertSame('100-Continue', $result['headers']['Expect']);
+	}
+
+	public function testSetsExpectHeaderIfBodyExactly1Mb() {
+		$request = Requests::post(httpbin('/post'), array(), str_repeat('x', 1048576), $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertSame('100-Continue', $result['headers']['Expect']);
+	}
+
+	/**
+	 * @small
+	 */
+	public function testSetsEmptyExpectHeaderIfBodySmallerThan1Mb() {
+		$request = Requests::post(httpbin('/post'), array(), str_repeat('x', 1048575), $this->getOptions());
+
+		$result = json_decode($request->body, true);
+
+		$this->assertFalse(isset($result['headers']['Expect']));
+	}
 }