Index: ext/session/sqlite3session.c
==================================================================
--- ext/session/sqlite3session.c
+++ ext/session/sqlite3session.c
@@ -1835,11 +1835,11 @@
   if( *pRc==SQLITE_OK && (size_t)(p->nAlloc-p->nBuf)<nByte ){
     u8 *aNew;
     i64 nNew = p->nAlloc ? p->nAlloc : 128;
     do {
       nNew = nNew*2;
-    }while( (nNew-p->nBuf)<nByte );
+    }while( (size_t)(nNew-p->nBuf)<nByte );
 
     aNew = (u8 *)sqlite3_realloc64(p->aBuf, nNew);
     if( 0==aNew ){
       *pRc = SQLITE_NOMEM;
     }else{