Index: src/wal.c
==================================================================
--- src/wal.c
+++ src/wal.c
@@ -2150,11 +2150,11 @@
           return rc;
         }
       }
     }
     if( mxI==0 ){
-      assert( rc==SQLITE_BUSY );
+      assert( rc==SQLITE_BUSY || (pWal->readOnly & WAL_SHM_RDONLY)!=0 );
       return rc==SQLITE_BUSY ? WAL_RETRY : SQLITE_READONLY_CANTLOCK;
     }
 
     rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
     if( rc ){