Index: src/window.c
==================================================================
--- src/window.c
+++ src/window.c
@@ -1594,19 +1594,21 @@
   **     // The frame always consists of 0 rows
   **     regStart = regSize;
   **   }
   **   regEnd = regEnd - regStart;
   */
-  if( pMWin->pEnd && pMWin->pStart && pMWin->eStart==TK_FOLLOWING ){
+  if( pMWin->pEnd && pMWin->eStart==TK_FOLLOWING ){
+    assert( pMWin->pStart!=0 );
     assert( pMWin->eEnd==TK_FOLLOWING );
     sqlite3VdbeAddOp3(v, OP_Ge, regStart, sqlite3VdbeCurrentAddr(v)+2, regEnd);
     VdbeCoverage(v);
     sqlite3VdbeAddOp2(v, OP_Copy, regSize, regStart);
     sqlite3VdbeAddOp3(v, OP_Subtract, regStart, regEnd, regEnd);
   }
 
-  if( pMWin->pEnd && pMWin->pStart && pMWin->eEnd==TK_PRECEDING ){
+  if( pMWin->pStart && pMWin->eEnd==TK_PRECEDING ){
+    assert( pMWin->pEnd!=0 );
     assert( pMWin->eStart==TK_PRECEDING );
     sqlite3VdbeAddOp3(v, OP_Le, regStart, sqlite3VdbeCurrentAddr(v)+3, regEnd);
     VdbeCoverage(v);
     sqlite3VdbeAddOp2(v, OP_Copy, regSize, regStart);
     sqlite3VdbeAddOp2(v, OP_Copy, regSize, regEnd);