Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -2176,23 +2176,33 @@
 
     for(iIn=0; iIn<nUri; iIn++) nByte += (zUri[iIn]=='&');
     zFile = sqlite3_malloc(nByte);
     if( !zFile ) return SQLITE_NOMEM;
 
-    /* Discard the scheme and authority segments of the URI. */
-    if( zUri[5]=='/' && zUri[6]=='/' ){
+    /* Mappings:
+    ** URI                            FILENAME
+    ** ---------------------------    ----------------------
+    ** file:abc/xyz                   abc/xyz
+    ** file:/abc/xyz                  /abc/xyz
+    ** file://abc/xyz                 //abc/xyz
+    ** file:///abc/xyz                /abc/xyz
+    ** file:////abc/xyz               //abc/xyz
+    ** file://///abc/xyz              //abc/xyz
+    ** file://localhost/xyz           /xyz
+    ** file:///c:/abc/xyz             /c:/abc/xyz    (winOpen() removes leading /)
+    */
+    iIn = 5;
+    if( strncmp(zUri+5, "///", 3)==0 ){
       iIn = 7;
-      while( zUri[iIn] && zUri[iIn]!='/' ) iIn++;
-
-      if( iIn!=7 && (iIn!=16 || memcmp("localhost", &zUri[7], 9)) ){
-        *pzErrMsg = sqlite3_mprintf("invalid uri authority: %.*s", 
-            iIn-7, &zUri[7]);
-        rc = SQLITE_ERROR;
-        goto parse_uri_out;
-      }
-    }else{
-      iIn = 5;
+      /* The following condition causes URIs with five leading / characters
+      ** like file://///host/path to be converted into UNCs like //host/path.
+      ** The correct URI for that UNC has only two or four leading / characters
+      ** file://host/path or file:////host/path.  But 5 leading slashes is a 
+      ** common error, we are told, so we handle it as a special case. */
+      if( strncmp(zUri+7, "///", 3)==0 ){ iIn++; }
+    }else if( strncmp(zUri+5, "//localhost/", 12)==0 ){
+      iIn = 16;
     }
 
     /* Copy the filename and any query parameters into the zFile buffer. 
     ** Decode %HH escape codes along the way. 
     **

Index: test/e_uri.test
==================================================================
--- test/e_uri.test
+++ test/e_uri.test
@@ -131,12 +131,10 @@
 if {$tcl_platform(platform) == "unix"} {
   set flags [list SQLITE_OPEN_READWRITE SQLITE_OPEN_CREATE SQLITE_OPEN_URI]
   foreach {tn uri error} "
     1  {file://localhost[test_pwd /]test.db}   {not an error}
     2  {file://[test_pwd /]test.db}            {not an error}
-    3  {file://x[test_pwd /]test.db}           {invalid uri authority: x}
-    4  {file://invalid[test_pwd /]test.db}     {invalid uri authority: invalid}
   " {
     do_test 2.$tn {
       set DB [sqlite3_open_v2 $uri $flags ""]
       set e [sqlite3_errmsg $DB]
       sqlite3_close $DB

Index: test/uri.test
==================================================================
--- test/uri.test
+++ test/uri.test
@@ -279,13 +279,10 @@
 catch {db close}
 foreach {tn uri res} {
   1     "file://localhost/PWD/test.db"   {not an error}
   2     "file:///PWD/test.db"            {not an error}
   3     "file:/PWD/test.db"              {not an error}
-  4     "file://l%6Fcalhost/PWD/test.db" {invalid uri authority: l%6Fcalhost}
-  5     "file://lbcalhost/PWD/test.db"   {invalid uri authority: lbcalhost}
-  6     "file://x/PWD/test.db"           {invalid uri authority: x}
 } {
 
   if {$tcl_platform(platform)=="windows"} {
     set uri  [string map [list PWD [string range [get_pwd] 3 end]] $uri]
   } else {