Index: src/vdbemem.c
==================================================================
--- src/vdbemem.c
+++ src/vdbemem.c
@@ -82,10 +82,12 @@
 
   if( !pMem->zMalloc || sqlite3MallocSize(pMem->zMalloc)<n ){
     n = (n>32?n:32);
     if( preserve && pMem->z==pMem->zMalloc ){
       pMem->z = pMem->zMalloc = sqlite3DbReallocOrFree(pMem->db, pMem->z, n);
+      if ( !pMem->z )
+        pMem->flags = MEM_Null;
       preserve = 0;
     }else{
       sqlite3_free(pMem->zMalloc);
       pMem->zMalloc = sqlite3DbMallocRaw(pMem->db, n);
     }