diff --git a/Misc/NEWS b/Misc/NEWS
index 313d913fe80..2a6dec82cb1 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -92,6 +92,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #26556: Update expat to 2.1.1, fixes CVE-2015-1283.
+
 - Fix TLS stripping vulnerability in smptlib, CVE-2016-0772.  Reported by Team
   Oststrom
 
diff --git a/Modules/expat/expat.h b/Modules/expat/expat.h
index 06b5de0f446..e8eefddc6d8 100644
--- a/Modules/expat/expat.h
+++ b/Modules/expat/expat.h
@@ -1040,7 +1040,7 @@ XML_GetFeatureList(void);
 */
 #define XML_MAJOR_VERSION 2
 #define XML_MINOR_VERSION 1
-#define XML_MICRO_VERSION 0
+#define XML_MICRO_VERSION 1
 
 #ifdef __cplusplus
 }
diff --git a/Modules/expat/xmlparse.c b/Modules/expat/xmlparse.c
index f35aa36ba8a..6a615082e11 100644
--- a/Modules/expat/xmlparse.c
+++ b/Modules/expat/xmlparse.c
@@ -1550,7 +1550,7 @@ XML_Parse(XML_Parser parser, const char *s, int len, int isFinal)
   else if (bufferPtr == bufferEnd) {
     const char *end;
     int nLeftOver;
-    enum XML_Error result;
+    enum XML_Status result;
     parseEndByteIndex += len;
     positionPtr = s;
     ps_finalBuffer = (XML_Bool)isFinal;
@@ -1678,6 +1678,10 @@ XML_ParseBuffer(XML_Parser parser, int len, int isFinal)
 void * XMLCALL
 XML_GetBuffer(XML_Parser parser, int len)
 {
+  if (len < 0) {
+    errorCode = XML_ERROR_NO_MEMORY;
+    return NULL;
+  }
   switch (ps_parsing) {
   case XML_SUSPENDED:
     errorCode = XML_ERROR_SUSPENDED;
@@ -1689,10 +1693,16 @@ XML_GetBuffer(XML_Parser parser, int len)
   }
 
   if (len > bufferLim - bufferEnd) {
-    /* FIXME avoid integer overflow */
-    int neededSize = len + (int)(bufferEnd - bufferPtr);
 #ifdef XML_CONTEXT_BYTES
-    int keep = (int)(bufferPtr - buffer);
+    int keep;
+#endif
+    int neededSize = len + (int)(bufferEnd - bufferPtr);
+    if (neededSize < 0) {
+      errorCode = XML_ERROR_NO_MEMORY;
+      return NULL;
+    }
+#ifdef XML_CONTEXT_BYTES
+    keep = (int)(bufferPtr - buffer);
 
     if (keep > XML_CONTEXT_BYTES)
       keep = XML_CONTEXT_BYTES;
@@ -1719,7 +1729,11 @@ XML_GetBuffer(XML_Parser parser, int len)
         bufferSize = INIT_BUFFER_SIZE;
       do {
         bufferSize *= 2;
-      } while (bufferSize < neededSize);
+      } while (bufferSize < neededSize && bufferSize > 0);
+      if (bufferSize <= 0) {
+        errorCode = XML_ERROR_NO_MEMORY;
+        return NULL;
+      }
       newBuf = (char *)MALLOC(bufferSize);
       if (newBuf == 0) {
         errorCode = XML_ERROR_NO_MEMORY;
@@ -2911,6 +2925,8 @@ storeAtts(XML_Parser parser, const ENCODING *enc,
         unsigned long uriHash = hash_secret_salt;
         ((XML_Char *)s)[-1] = 0;  /* clear flag */
         id = (ATTRIBUTE_ID *)lookup(parser, &dtd->attributeIds, s, 0);
+        if (!id || !id->prefix)
+          return XML_ERROR_NO_MEMORY;
         b = id->prefix->binding;
         if (!b)
           return XML_ERROR_UNBOUND_PREFIX;
@@ -5475,6 +5491,8 @@ getAttributeId(XML_Parser parser, const ENCODING *enc,
             return NULL;
           id->prefix = (PREFIX *)lookup(parser, &dtd->prefixes, poolStart(&dtd->pool),
                                         sizeof(PREFIX));
+          if (!id->prefix)
+            return NULL;
           if (id->prefix->name == poolStart(&dtd->pool))
             poolFinish(&dtd->pool);
           else
diff --git a/Modules/expat/xmltok.c b/Modules/expat/xmltok.c
index b9cd7a45130..bf09dfc72b9 100644
--- a/Modules/expat/xmltok.c
+++ b/Modules/expat/xmltok.c
@@ -1584,7 +1584,7 @@ initScan(const ENCODING * const *encodingTable,
       if (ptr[0] == '\0') {
         /* 0 isn't a legal data character. Furthermore a document
            entity can only start with ASCII characters.  So the only
-           way this can fail to be big-endian UTF-16 is if it is an
+           way this can fail to be big-endian UTF-16 if it it's an
            external parsed general entity that's labelled as
            UTF-16LE.
         */