diff --git a/system/libraries/Email.php b/system/libraries/Email.php
index 66b5803..57693e1 100644
--- a/system/libraries/Email.php
+++ b/system/libraries/Email.php
@@ -2126,12 +2126,32 @@
 	protected function _send_data($data)
 	{
 		$data .= $this->newline;
-		for ($written = 0, $length = strlen($data); $written < $length; $written += $result)
+		for ($written = $timestamp = 0, $length = strlen($data); $written < $length; $written += $result)
 		{
 			if (($result = fwrite($this->_smtp_connect, substr($data, $written))) === FALSE)
 			{
 				break;
 			}
+			// See https://bugs.php.net/bug.php?id=39598 and http://php.net/manual/en/function.fwrite.php#96951
+			elseif ($result === 0)
+			{
+				if ($timestamp === 0)
+				{
+					$timestamp = time();
+				}
+				elseif ($timestamp < (time() - $this->smtp_timeout))
+				{
+					$result = FALSE;
+					break;
+				}
+
+				usleep(250000);
+				continue;
+			}
+			else
+			{
+				$timestamp = 0;
+			}
 		}
 
 		if ($result === FALSE)
diff --git a/system/libraries/Xmlrpc.php b/system/libraries/Xmlrpc.php
index 8fbc18f..55555f5 100644
--- a/system/libraries/Xmlrpc.php
+++ b/system/libraries/Xmlrpc.php
@@ -735,12 +735,32 @@
 			.'Content-Length: '.strlen($msg->payload).$r.$r
 			.$msg->payload;
 
-		for ($written = 0, $length = strlen($op); $written < $length; $written += $result)
+		for ($written = $timestamp = 0, $length = strlen($op); $written < $length; $written += $result)
 		{
 			if (($result = fwrite($fp, substr($op, $written))) === FALSE)
 			{
 				break;
 			}
+			// See https://bugs.php.net/bug.php?id=39598 and http://php.net/manual/en/function.fwrite.php#96951
+			elseif ($result === 0)
+			{
+				if ($timestamp === 0)
+				{
+					$timestamp = time();
+				}
+				elseif ($timestamp < (time() - $this->timeout))
+				{
+					$result = FALSE;
+					break;
+				}
+
+				usleep(250000);
+				continue;
+			}
+			else
+			{
+				$timestamp = 0;
+			}
 		}
 
 		if ($result === FALSE)
diff --git a/user_guide_src/source/changelog.rst b/user_guide_src/source/changelog.rst
index 034fa9a..46d19bf 100644
--- a/user_guide_src/source/changelog.rst
+++ b/user_guide_src/source/changelog.rst
@@ -42,6 +42,7 @@
 -  Fixed a bug (#3890) - :doc:`Input Library <libraries/input>` method ``get_request_header()`` treated header names as case-sensitive.
 -  Fixed a bug (#3903) - :doc:`Form Validation Library <libraries/form_validation>` ignored "unnamed" closure validation rules.
 -  Fixed a bug (#3904) - :doc:`Form Validation Library <libraries/form_validation>` ignored "named" callback rules when the field is empty and there's no 'required' rule.
+-  Fixed a bug (#3922) - :doc:`Email <libraries/email>` and :doc:`XML-RPC <libraries/xmlrpc>` libraries could enter an infinite loop due to `PHP bug #39598 <https://bugs.php.net/bug.php?id=39598>`_.
 
 Version 3.0.0
 =============