Index: src/sqliteInt.h
==================================================================
--- src/sqliteInt.h
+++ src/sqliteInt.h
@@ -1581,10 +1581,11 @@
 #define SQLITE_CursorHints    0x0400   /* Add OP_CursorHint opcodes */
 #define SQLITE_Stat34         0x0800   /* Use STAT3 or STAT4 data */
    /* TH3 expects the Stat34  ^^^^^^ value to be 0x0800.  Don't change it */
 #define SQLITE_PushDown       0x1000   /* The push-down optimization */
 #define SQLITE_SimplifyJoin   0x2000   /* Convert LEFT JOIN to JOIN */
+#define SQLITE_SkipScan       0x4000   /* Skip-scans */
 #define SQLITE_AllOpts        0xffff   /* All optimizations */
 
 /*
 ** Macros for testing whether or not optimizations are enabled or disabled.
 */

Index: src/test1.c
==================================================================
--- src/test1.c
+++ src/test1.c
@@ -6952,10 +6952,11 @@
     { "order-by-idx-join",   SQLITE_OrderByIdxJoin },
     { "transitive",          SQLITE_Transitive     },
     { "omit-noop-join",      SQLITE_OmitNoopJoin   },
     { "stat3",               SQLITE_Stat34         },
     { "stat4",               SQLITE_Stat34         },
+    { "skip-scan",           SQLITE_SkipScan       },
   };
 
   if( objc!=4 ){
     Tcl_WrongNumArgs(interp, 1, objv, "DB OPT BOOLEAN");
     return TCL_ERROR;

Index: src/where.c
==================================================================
--- src/where.c
+++ src/where.c
@@ -2670,10 +2670,11 @@
   ** more expensive.  */
   assert( 42==sqlite3LogEst(18) );
   if( saved_nEq==saved_nSkip
    && saved_nEq+1<pProbe->nKeyCol
    && pProbe->noSkipScan==0
+   && OptimizationEnabled(db, SQLITE_SkipScan)
    && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */
    && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
   ){
     LogEst nIter;
     pNew->u.btree.nEq++;

Index: test/skipscan1.test
==================================================================
--- test/skipscan1.test
+++ test/skipscan1.test
@@ -335,6 +335,14 @@
   ANALYZE sqlite_master;
   EXPLAIN QUERY PLAN
   SELECT * FROM t9a WHERE b IN (SELECT x FROM t9b WHERE y!=5);
 } {/USING INDEX t9a_ab .ANY.a. AND b=./}
 
+
+optimization_control db skip-scan 0
+do_execsql_test skipscan1-9.3 {
+  EXPLAIN QUERY PLAN
+  SELECT  * FROM t9a WHERE b IN (SELECT x FROM t9b WHERE y!=5);
+} {/{SCAN TABLE t9a}/}
+optimization_control db skip-scan 1
+
 finish_test