diff --git a/development/scons/scons_manifest.py b/development/scons/scons_manifest.py
index ed1088340c..8c92a83224 100644
--- a/development/scons/scons_manifest.py
+++ b/development/scons/scons_manifest.py
@@ -341,7 +341,6 @@ src_support_files = Split('''
     kill.cpp
     lassert.cpp
     lstrings.cpp
-    lyxsum.cpp
     lyxtime.cpp
     os.cpp
     qstring_helpers.cpp
diff --git a/src/support/FileName.cpp b/src/support/FileName.cpp
index d87ab63f4b..43a6f1eda7 100644
--- a/src/support/FileName.cpp
+++ b/src/support/FileName.cpp
@@ -16,6 +16,7 @@
 #include "support/convert.h"
 #include "support/debug.h"
 #include "support/filetools.h"
+#include "support/lassert.h"
 #include "support/lstrings.h"
 #include "support/qstring_helpers.h"
 #include "support/os.h"
@@ -30,13 +31,15 @@
 #include <QTemporaryFile>
 #include <QTime>
 
-#include "support/lassert.h"
+#include <boost/crc.hpp>
 #include <boost/scoped_array.hpp>
 
+#include <algorithm>
+#include <iterator>
+#include <fstream>
+#include <iomanip>
 #include <map>
 #include <sstream>
-#include <fstream>
-#include <algorithm>
 
 #ifdef HAVE_SYS_TYPES_H
 # include <sys/types.h>
@@ -75,11 +78,85 @@ extern "C" int mkstemp(char *);
 # endif
 #endif
 
+// Various implementations of sum(), depending on what methods
+// are available. Order is faster to slowest.
+#if defined(HAVE_MMAP) && defined(HAVE_MUNMAP)
+#define SUM_WITH_MMAP
+#ifdef HAVE_SYS_TYPES_H
+# include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_STAT_H
+# include <sys/stat.h>
+#endif
+#include <fcntl.h>
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+#include <sys/mman.h>
+#endif // SUM_WITH_MMAP
+
 using namespace std;
 
+// OK, this is ugly, but it is the only workaround I found to compile
+// with gcc (any version) on a system which uses a non-GNU toolchain.
+// The problem is that gcc uses a weak symbol for a particular
+// instantiation and that the system linker usually does not
+// understand those weak symbols (seen on HP-UX, tru64, AIX and
+// others). Thus we force an explicit instanciation of this particular
+// template (JMarc)
+template struct boost::detail::crc_table_t<32, 0x04C11DB7, true>;
+
 namespace lyx {
 namespace support {
 
+static unsigned long sum(char const * file)
+{
+#ifdef SUM_WITH_MMAP
+	//LYXERR(Debug::FILES, "lyx::sum() using mmap (lightning fast)");
+
+	int fd = open(file, O_RDONLY);
+	if (!fd)
+		return 0;
+
+	struct stat info;
+	fstat(fd, &info);
+
+	void * mm = mmap(0, info.st_size, PROT_READ,
+			 MAP_PRIVATE, fd, 0);
+	// Some platforms have the wrong type for MAP_FAILED (compaq cxx).
+	if (mm == reinterpret_cast<void*>(MAP_FAILED)) {
+		close(fd);
+		return 0;
+	}
+
+	char * beg = static_cast<char*>(mm);
+	char * end = beg + info.st_size;
+
+	boost::crc_32_type crc;
+	crc.process_block(beg, end);
+	unsigned long result = crc.checksum();
+
+	munmap(mm, info.st_size);
+	close(fd);
+
+	return result;
+
+#else // no SUM_WITH_MMAP
+
+	//LYXERR(Debug::FILES, "lyx::sum() using istreambuf_iterator (fast)");
+	ifstream ifs(file, ios_base::in | ios_base::binary);
+	if (!ifs)
+		return 0;
+
+	istreambuf_iterator<char> beg(ifs);
+	istreambuf_iterator<char> end;
+	boost::crc_32_type crc;
+	crc = for_each(beg, end, crc);
+	return crc.checksum();
+
+#endif // SUM_WITH_MMAP
+}
+
 
 /////////////////////////////////////////////////////////////////////
 //
@@ -431,8 +508,6 @@ bool FileName::chdir() const
 }
 
 
-extern unsigned long sum(char const * file);
-
 unsigned long FileName::checksum() const
 {
 	if (!exists()) {
diff --git a/src/support/Makefile.am b/src/support/Makefile.am
index 1c1f8a038d..1b5f7086e0 100644
--- a/src/support/Makefile.am
+++ b/src/support/Makefile.am
@@ -72,7 +72,6 @@ liblyxsupport_la_SOURCES = \
 	lyxlib.h \
 	lyxtime.cpp \
 	lyxtime.h \
-	lyxsum.cpp \
 	Messages.cpp \
 	Messages.h \
 	os.cpp \
diff --git a/src/support/lyxsum.cpp b/src/support/lyxsum.cpp
deleted file mode 100644
index 0f15491802..0000000000
--- a/src/support/lyxsum.cpp
+++ /dev/null
@@ -1,133 +0,0 @@
-/**
- * \file lyxsum.cpp
- * This file is part of LyX, the document processor.
- * Licence details can be found in the file COPYING.
- *
- * \author Lars Gullik Bjønnes
- *
- * Full author contact details are available in file CREDITS.
- */
-
-#include <config.h>
-
-#include "support/debug.h"
-
-#include <boost/crc.hpp>
-
-#include <algorithm>
-#include <iomanip>
-
-using namespace std;
-
-// OK, this is ugly, but it is the only workaround I found to compile
-// with gcc (any version) on a system which uses a non-GNU toolchain.
-// The problem is that gcc uses a weak symbol for a particular
-// instantiation and that the system linker usually does not
-// understand those weak symbols (seen on HP-UX, tru64, AIX and
-// others). Thus we force an explicit instanciation of this particular
-// template (JMarc)
-template struct boost::detail::crc_table_t<32, 0x04C11DB7, true>;
-
-// Various implementations of lyx::sum(), depending on what methods
-// are available. Order is faster to slowest.
-#if defined(HAVE_MMAP) && defined(HAVE_MUNMAP)
-
-#ifdef HAVE_SYS_TYPES_H
-# include <sys/types.h>
-#endif
-#ifdef HAVE_SYS_STAT_H
-# include <sys/stat.h>
-#endif
-#include <fcntl.h>
-#ifdef HAVE_UNISTD_H
-# include <unistd.h>
-#endif
-
-#include <sys/mman.h>
-
-
-namespace lyx {
-namespace support {
-
-unsigned long sum(char const * file)
-{
-	//LYXERR(Debug::FILES, "lyx::sum() using mmap (lightning fast)");
-
-	int fd = open(file, O_RDONLY);
-	if (!fd)
-		return 0;
-
-	struct stat info;
-	fstat(fd, &info);
-
-	void * mm = mmap(0, info.st_size, PROT_READ,
-			 MAP_PRIVATE, fd, 0);
-	// Some platforms have the wrong type for MAP_FAILED (compaq cxx).
-	if (mm == reinterpret_cast<void*>(MAP_FAILED)) {
-		close(fd);
-		return 0;
-	}
-
-	char * beg = static_cast<char*>(mm);
-	char * end = beg + info.st_size;
-
-	boost::crc_32_type crc;
-	crc.process_block(beg, end);
-	unsigned long result = crc.checksum();
-
-	munmap(mm, info.st_size);
-	close(fd);
-
-	return result;
-}
-
-} // namespace support
-} // namespace lyx
-
-#else // No mmap
-
-#include <fstream>
-#include <iterator>
-
-namespace {
-
-template<typename InputIterator>
-inline
-unsigned long do_crc(InputIterator first, InputIterator last)
-{
-	boost::crc_32_type crc;
-	crc = for_each(first, last, crc);
-	return crc.checksum();
-}
-
-} // namespace anon
-
-
-namespace lyx {
-namespace support {
-
-
-unsigned long sum(char const * file)
-{
-	ifstream ifs(file, ios_base::in | ios_base::binary);
-	if (!ifs)
-		return 0;
-
-#if HAVE_DECL_ISTREAMBUF_ITERATOR
-	//LYXERR(Debug::FILES, "lyx::sum() using istreambuf_iterator (fast)");
-	istreambuf_iterator<char> beg(ifs);
-	istreambuf_iterator<char> end;
-#else
-	//LYXERR(Debug::FILES, "lyx::sum() using istream_iterator (slow as a snail)");
-	ifs.unsetf(ios::skipws);
-	istream_iterator<char> beg(ifs);
-	istream_iterator<char> end;
-#endif
-
-	return do_crc(beg,end);
-}
-
-} // namespace support
-} // namespace lyx
-
-#endif // mmap