diff --git a/parser.c b/parser.c
index b41dcc3..e415339 100644
--- a/parser.c
+++ b/parser.c
@@ -10130,12 +10130,8 @@ xmlParseDocument(xmlParserCtxtPtr ctxt) {
     /*
      * Check for the XMLDecl in the Prolog.
      * do not GROW here to avoid the detected encoder to decode more
-     * than just the first line, unless the amount of data is really
-     * too small to hold "<?xml version="1.0" encoding="foo"
+     * than just the first line
      */
-    if ((ctxt->input->end - ctxt->input->cur) < 35) {
-       GROW;
-    }
     if ((CMP5(CUR_PTR, '<', '?', 'x', 'm', 'l')) && (IS_BLANK_CH(NXT(5)))) {
 
 	/*
diff --git a/xmlIO.c b/xmlIO.c
index c03ac43..1e7d213 100644
--- a/xmlIO.c
+++ b/xmlIO.c
@@ -3149,7 +3149,11 @@ xmlParserInputBufferGrow(xmlParserInputBufferPtr in, int len) {
      * Call the read method for this I/O type.
      */
     if (in->readcallback != NULL) {
-	res = in->readcallback(in->context, &buffer[0], len);
+        nbchars = 0;
+        while (len && (res = in->readcallback(in->context, &buffer[nbchars], len)) > 0) {
+           nbchars += res;
+           len -= res;
+        }
 	if (res <= 0)
 	    in->readcallback = endOfInput;
     } else {
@@ -3160,7 +3164,7 @@ xmlParserInputBufferGrow(xmlParserInputBufferPtr in, int len) {
     if (res < 0) {
 	return(-1);
     }
-    len = res;
+    len = nbchars;
     if (in->encoder != NULL) {
         unsigned int use;