Index: src/test_multiplex.c
==================================================================
--- src/test_multiplex.c
+++ src/test_multiplex.c
@@ -94,30 +94,18 @@
 */
 #ifndef SQLITE_MULTIPLEX_CHUNK_SIZE
 # define SQLITE_MULTIPLEX_CHUNK_SIZE 2147418112
 #endif
 
-/* Default limit on number of chunks.  Care should be taken
-** so that values for chunks numbers fit in the SQLITE_MULTIPLEX_EXT_FMT
-** format specifier. It may be changed by calling
+/* Default limit on number of chunks.
+** May be changed by calling
 ** the xFileControl() interface.
 */
 #ifndef SQLITE_MULTIPLEX_MAX_CHUNKS
 # define SQLITE_MULTIPLEX_MAX_CHUNKS 32
 #endif
 
-/* If SQLITE_MULTIPLEX_EXT_OVWR is defined, the 
-** last SQLITE_MULTIPLEX_EXT_SZ characters of the 
-** filename will be overwritten, otherwise, the 
-** multiplex extension is simply appended to the filename.
-** Ex.  (undefined) test.db -> test.db01
-**      (defined)   test.db -> test.01
-** Chunk 0 does not have a modified extension.
-*/
-#define SQLITE_MULTIPLEX_EXT_FMT    "%02d"
-#define SQLITE_MULTIPLEX_EXT_SZ     2
-
 /************************ Object Definitions ******************************/
 
 /* Forward declaration of all object types */
 typedef struct multiplexGroup multiplexGroup;
 typedef struct multiplexConn multiplexConn;
@@ -302,24 +290,22 @@
     pGroup->nReal = iChunk+1;
   }
   if( pGroup->aReal[iChunk].z==0 ){
     char *z;
     int n = pGroup->nName;
-    pGroup->aReal[iChunk].z = z = sqlite3_malloc( n+3 );
+    pGroup->aReal[iChunk].z = z = sqlite3_malloc( n+4 );
     if( z==0 ){
       return SQLITE_NOMEM;
     }
     memcpy(z, pGroup->zName, n+1);
     if( iChunk>0 ){
 #ifdef SQLITE_ENABLE_8_3_NAMES
-      if( n>3 && z[n-3]=='.' ){
-        n--;
-      }else if( n>4 && z[n-4]=='.' ){
-        n -= 2;
-      }
+      int i;
+      for(i=n-1; i>0 && i>=n-4 && z[i]!='.'; i--){}
+      if( i>=n-4 ) n = i+1;
 #endif
-      sqlite3_snprintf(3,&z[n],"%02d",iChunk);
+      sqlite3_snprintf(4,&z[n],"%03d",iChunk);
     }
   }
   return SQLITE_OK;
 }
 

Index: test/multiplex.test
==================================================================
--- test/multiplex.test
+++ test/multiplex.test
@@ -22,11 +22,11 @@
 # SQLITE_MULTIPLEX_EXT_OVWR is defined, then
 # it overwrites the last 2 bytes of the 
 # file name with the chunk number.
 proc multiplex_name {name chunk} {
   if {$chunk==0} { return $name }
-  set num [format "%02d" $chunk]
+  set num [format "%03d" $chunk]
   ifcapable {multiplex_ext_overwrite} {
     set name [string range $name 0 [expr [string length $name]-2-1]]
   }
   return $name$num
 }