--- old/src/share/vm/logging/logStream.cpp	2017-06-21 17:45:59.011284600 +0200
+++ new/src/share/vm/logging/logStream.cpp	2017-06-21 17:45:58.112609800 +0200
@@ -41,7 +41,7 @@
 
 void LogStream::LineBuffer::ensure_cap(size_t atleast) {
   assert(_cap >= sizeof(_smallbuf), "sanity");
-  if (_cap < atleast) { 
+  if (_cap < atleast) {
     const size_t newcap = MAX2(_cap * 2, atleast * 2);
     char* const newbuf = (char*) os::malloc(newcap, mtLogging);
     if (_pos > 0) { // preserve old content
@@ -58,20 +58,20 @@
 
 void LogStream::LineBuffer::append(const char* s, size_t len) {
   assert(_buf[_pos] == '\0', "sanity");
-  const size_t remaining = _cap - _pos;
-  ensure_cap(remaining + len + 1);
+  ensure_cap(_pos + len + 1);
+  assert(_cap >= _pos + len + 1, "sanity");
   memcpy(_buf + _pos, s, len);
   _pos += len;
   _buf[_pos] = '\0';
 }
-    
+
 void LogStream::LineBuffer::reset() {
   _pos = 0;
   _buf[_pos] = '\0';
 }
 
 void LogStream::write(const char* s, size_t len) {
-  
+
   if (len > 0 && s[len - 1] == '\n') {
     _current_line.append(s, len - 1); // omit the newline.
     _log_handle.print("%s", _current_line.ptr());