Index: src/file.c
==================================================================
--- src/file.c
+++ src/file.c
@@ -644,10 +644,11 @@
 }
 
 /*
 ** Simplify a filename by
 **
+**  * Remove extended path prefix on windows and cygwin
 **  * Convert all \ into / on windows and cygwin
 **  * removing any trailing and duplicate /
 **  * removing /./
 **  * removing /A/../
 **
@@ -654,17 +655,27 @@
 ** Changes are made in-place.  Return the new name length.
 ** If the slash parameter is non-zero, the trailing slash, if any,
 ** is retained.
 */
 int file_simplify_name(char *z, int n, int slash){
-  int i, j;
+  int i = 1, j;
   if( n<0 ) n = strlen(z);
 
-  /* On windows and cygwin convert all \ characters to / */
+  /* On windows and cygwin convert all \ characters to /
+   * and remove extended path prefix if present */
 #if defined(_WIN32) || defined(__CYGWIN__)
-  for(i=0; i<n; i++){
-    if( z[i]=='\\' ) z[i] = '/';
+  for(j=0; j<n; j++){
+    if( z[j]=='\\' ) z[j] = '/';
+  }
+  if( n>3 && !memcmp(z, "//?/", 4) ){
+    if( fossil_strnicmp(z+4,"UNC", 3) ){
+      i += 4;
+      z[0] = z[4];
+    }else{
+      i += 6;
+      z[0] = '/';
+    }
   }
 #endif
 
   /* Removing trailing "/" characters */
   if( !slash ){
@@ -671,11 +682,11 @@
     while( n>1 && z[n-1]=='/' ){ n--; }
   }
 
   /* Remove duplicate '/' characters.  Except, two // at the beginning
   ** of a pathname is allowed since this is important on windows. */
-  for(i=j=1; i<n; i++){
+  for(j=1; i<n; i++){
     z[j++] = z[i];
     while( z[i]=='/' && i<n-1 && z[i+1]=='/' ) i++;
   }
   n = j;
 

Index: src/utf8.c
==================================================================
--- src/utf8.c
+++ src/utf8.c
@@ -190,11 +190,12 @@
 **
 */
 void *fossil_utf8_to_filename(const char *zUtf8){
 #ifdef _WIN32
   int nChar = MultiByteToWideChar(CP_UTF8, 0, zUtf8, -1, 0, 0);
-  wchar_t *zUnicode = sqlite3_malloc( nChar * 2 );
+  /* Overallocate 6 chars, making some room for extended paths */
+  wchar_t *zUnicode = sqlite3_malloc( (nChar+6) * sizeof(wchar_t) );
   wchar_t *wUnicode = zUnicode;
   if( zUnicode==0 ){
     return 0;
   }
   MultiByteToWideChar(CP_UTF8, 0, zUtf8, -1, zUnicode, nChar);
@@ -207,17 +208,35 @@
     wUnicode[0] = wUnicode[1] = wUnicode[3] = '\\';
     zUtf8 += 4;
     wUnicode += 4;
   }
   /*
-  ** If (remainder of) path starts with "<drive>:/" or "<drive>:\",
-  ** leave the ':' intact
-  */
+  ** If there is no "\\?\" prefix but there is a drive or UNC
+  ** path prefix and the path is larger than MAX_PATH chars,
+  ** no Win32 API function can handle that unless it is
+  ** prefixed with the extended path prefix. See:
+  ** <http://msdn.microsoft.com/en-us/library/aa365247(VS.85).aspx#maxpath>
+  **/
   if( fossil_isalpha(zUtf8[0]) && zUtf8[1]==':'
-           && (zUtf8[2]=='\\' || zUtf8[2]=='/')) {
+           && (zUtf8[2]=='\\' || zUtf8[2]=='/') ){
+    if( wUnicode==zUnicode && nChar>MAX_PATH){
+      memmove(wUnicode+4, wUnicode, nChar*sizeof(wchar_t));
+      memcpy(wUnicode, L"\\\\?\\", 4*sizeof(wchar_t));
+      wUnicode += 4;
+    }
+    /*
+    ** If (remainder of) path starts with "<drive>:/" or "<drive>:\",
+    ** leave the ':' intact but translate the backslash to a slash.
+    */
     wUnicode[2] = '\\';
     wUnicode += 3;
+  }else if( wUnicode==zUnicode && nChar>MAX_PATH
+            && (zUtf8[0]=='\\' || zUtf8[0]=='/')
+            && (zUtf8[1]=='\\' || zUtf8[1]=='/') && zUtf8[2]!='?'){
+    memmove(wUnicode+6, wUnicode, nChar*sizeof(wchar_t));
+    memcpy(wUnicode, L"\\\\?\\UNC", 7*sizeof(wchar_t));
+    wUnicode += 7;
   }
   /*
   ** In the remainder of the path, translate invalid characters to
   ** characters in the Unicode private use area. This is what makes
   ** Win32 fossil.exe work well in a Cygwin environment even when a

Index: test/file1.test
==================================================================
--- test/file1.test
+++ test/file1.test
@@ -33,5 +33,10 @@
 simplify-name 103 a/b a/b /a/b /a/b a///b a/b ///a///b///// //a/b
 simplify-name 104 a/b/../c/ a/c /a/b/../c /a/c /a/b//../c /a/c /a/b/..///c /a/c
 simplify-name 105 a/b/../../x/y x/y /a/b/../../x/y /x/y
 simplify-name 106 a/b/../../../x/y ../x/y /a/b/../../../x/y /../x/y
 simplify-name 107 a/./b/.././../x/y x/y a//.//b//..//.//..//x//y/// x/y
+
+if {$::tcl_platform(os)=="Windows NT"} {
+  simplify-name 108 //?/a:/a/b a:/a/b //?/UNC/a/b //a/b //?/ {}
+  simplify-name 109 \\\\?\\a:\\a\\b a:/a/b \\\\?\\UNC\\a\\b //a/b \\\\?\\ {}
+}