diff --git a/expat/lib/expat.h b/expat/lib/expat.h
index d0d6015a..3ba61304 100644
--- a/expat/lib/expat.h
+++ b/expat/lib/expat.h
@@ -130,7 +130,9 @@ enum XML_Error {
   /* Added in 2.3.0. */
   XML_ERROR_NO_BUFFER,
   /* Added in 2.4.0. */
-  XML_ERROR_AMPLIFICATION_LIMIT_BREACH
+  XML_ERROR_AMPLIFICATION_LIMIT_BREACH,
+  /* Added in 2.6.4. */
+  XML_ERROR_NOT_STARTED,
 };
 
 enum XML_Content_Type {
diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
index d9285b21..fa02537f 100644
--- a/expat/lib/xmlparse.c
+++ b/expat/lib/xmlparse.c
@@ -2234,6 +2234,9 @@ XML_StopParser(XML_Parser parser, XML_Bool resumable) {
   if (parser == NULL)
     return XML_STATUS_ERROR;
   switch (parser->m_parsingStatus.parsing) {
+  case XML_INITIALIZED:
+    parser->m_errorCode = XML_ERROR_NOT_STARTED;
+    return XML_STATUS_ERROR;
   case XML_SUSPENDED:
     if (resumable) {
       parser->m_errorCode = XML_ERROR_SUSPENDED;
@@ -2519,6 +2522,9 @@ XML_ErrorString(enum XML_Error code) {
   case XML_ERROR_AMPLIFICATION_LIMIT_BREACH:
     return XML_L(
         "limit on input amplification factor (from DTD and entities) breached");
+  /* Added in 2.6.4. */
+  case XML_ERROR_NOT_STARTED:
+    return XML_L("parser not started");
   }
   return NULL;
 }