diff --git a/ChangeLog b/ChangeLog
index 7802866a25..849f5142a6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,14 @@
+2001-05-30  Lars Gullik Bjønnes  <larsbj@birdstep.com>
+
+	* configure.in:
+	* src/support/lyxsum.C (sum): use istreambuf_iterator when
+	available. 
+
+2001-05-29  Lars Gullik Bjønnes  <larsbj@birdstep.com>
+
+	* src/support/lyxsum.C (sum): don't use sstream anymore, use
+	istream_iterator directly instead.
+
 2001-05-23  Angus Leeming <a.leeming@ic.ac.uk>
 
 	* src/frontends/xforms/FormInset.C (createInset): fixed bug
diff --git a/configure.in b/configure.in
index ee988380a7..0655ed4241 100644
--- a/configure.in
+++ b/configure.in
@@ -253,6 +253,7 @@ fi
 AC_CHECK_FUNCS(snprintf vsnprintf)
 LYX_CHECK_DECL(snprintf, stdio.h)
 LYX_CHECK_DECL(vsnprintf, stdio.h)
+LYX_CHECK_DECL(istreambuf_iterator, iterator)
 
 AC_CHECK_FUNCS(memmove memset strchr putenv setenv mkfifo \
   mkstemp mktemp)
diff --git a/src/support/lyxsum.C b/src/support/lyxsum.C
index 8980a3f8ae..d9ba88db08 100644
--- a/src/support/lyxsum.C
+++ b/src/support/lyxsum.C
@@ -16,8 +16,7 @@
 #include <config.h>
 
 #include <fstream>
-
-#include "Lsstream.h"
+#include <iterator>
 
 #include "support/lyxlib.h"
 
@@ -108,14 +107,20 @@ unsigned long do_crc(InputIterator first, InputIterator last)
 // And this would be the file interface.
 unsigned long lyx::sum(string const & file)
 {
-	ifstream ifs(file.c_str());
+	std::ifstream ifs(file.c_str());
 	if (!ifs) return 0;
-	ifs.unsetf(ios::skipws);
-	ostringstream ostr;
-	ostr << ifs.rdbuf();
-	// The .c_str() is here in case we use our lyxstring class
-	// instead of standard string. 
-	string w = ostr.str().c_str();
-	return do_crc(w.begin(), w.end());
+	
+#ifdef HAVE_DECL_ISTREAMBUF_ITERATOR
+	// This is a lot faster...
+	std::istreambuf_iterator<char> beg(ifs);
+	std::istreambuf_iterator<char> end;
+#else
+	// than this.
+	ifs.unsetf(std::ios::skipws);
+	std::istream_iterator<char> beg(ifs);
+	std::istream_iterator<char> end;
+#endif
+
+	return do_crc(beg, end);
 }