Index: src/build.c
==================================================================
--- src/build.c
+++ src/build.c
@@ -714,11 +714,14 @@
 int sqlite3FindDbName(sqlite3 *db, const char *zName){
   int i = -1;         /* Database number */
   if( zName ){
     Db *pDb;
     for(i=(db->nDb-1), pDb=&db->aDb[i]; i>=0; i--, pDb--){
-      if( 0==sqlite3StrICmp(pDb->zDbSName, zName) ) break;
+      if( 0==sqlite3_stricmp(pDb->zDbSName, zName) ) break;
+      /* "main" is always an acceptable alias for the primary database
+      ** even if it has been renamed using SQLITE_DBCONFIG_MAINDBNAME. */
+      if( i==0 && 0==sqlite3_stricmp("main", zName) ) break;
     }
   }
   return i;
 }
 

Index: src/main.c
==================================================================
--- src/main.c
+++ src/main.c
@@ -3924,19 +3924,12 @@
 
 /*
 ** Return the Btree pointer identified by zDbName.  Return NULL if not found.
 */
 Btree *sqlite3DbNameToBtree(sqlite3 *db, const char *zDbName){
-  int i;
-  for(i=0; i<db->nDb; i++){
-    if( db->aDb[i].pBt
-     && (zDbName==0 || sqlite3StrICmp(zDbName, db->aDb[i].zDbSName)==0)
-    ){
-      return db->aDb[i].pBt;
-    }
-  }
-  return 0;
+  int iDb = zDbName ? sqlite3FindDbName(db, zDbName) : 0;
+  return iDb<0 ? 0 : db->aDb[iDb].pBt;
 }
 
 /*
 ** Return the filename of the database associated with a database
 ** connection.