diff --git a/manifest b/manifest
index 1ce91e738e..b77b1484ce 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Updates\sto\sthe\sMakefiles\sfor\sMSVC.
-D 2017-10-14T19:54:06.773
+C In\sthe\squery\splanner,\sdo\snot\sconsider\sindex\sX\sto\sbe\sa\sproper\ssubset\sof\s\nindex\sY\sif\sX\sis\sa\scovering\sindex\sbut\sY\sis\snot.
+D 2017-10-15T22:16:25.229
 F Makefile.in e016061b23e60ac9ec27c65cb577292b6bde0307ca55abd874ab3487b3b1beb2
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 37740aba9c4bb359c627eadccf1cfd7be4f5f847078723777ea7763969e533b1
@@ -544,7 +544,7 @@ F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
 F src/wal.c 839db09792fead5052bb35e533fa485e134913d547d05b5f42e537b73e63f07a
 F src/wal.h 8de5d2d3de0956d6f6cb48c83a4012d5f227b8fe940f3a349a4b7e85ebcb492a
 F src/walker.c 3ccfa8637f95355bff61144e01a615b8ef26f79c312880848da73f03367da1e6
-F src/where.c 049522adcf5426f1a8c3ed07be15e1ffa3266afd34e8e7bee64b63e2fbfad0b5
+F src/where.c 248f0dc6085b37b4b2ccad2de06b90f1a48b1932403ab0ad9100a1f2a6990763
 F src/whereInt.h 82c04c5075308abbac59180c8bad5ecb45b07453981f60a53f3c7dee21e1e971
 F src/wherecode.c e8c2ece5843ea56e6c90277d421f2d628f3f7b7c976642369cc519f008e1d2b1
 F src/whereexpr.c afcac9cccfc0fdaccbdda94034a398947b6dc47dbf821c1b496261722832a6a4
@@ -568,7 +568,7 @@ F test/analyze5.test 765c4e284aa69ca172772aa940946f55629bc8c4
 F test/analyze6.test f1c552ce39cca4ec922a7e4e0e5d0203d6b3281f
 F test/analyze7.test bb1409afc9e8629e414387ef048b8e0e3e0bdc4f
 F test/analyze8.test c05a461d0a6b05991106467d0c47480f2e709c82
-F test/analyze9.test b817b8e798315fc65b820a5463f73ad5f48ed8dd
+F test/analyze9.test dac0bdc7eab965b9ad639ca83564d98717aaf13ce5a776f23d9a3680238cecd8
 F test/analyzeA.test 3335697f6700c7052295cfd0067fc5b2aacddf9a
 F test/analyzeB.test a4c1c3048f6d9e090eb76e83eecb18bcf6d31a70
 F test/analyzeC.test 555a6cc388b9818b6eda6df816f01ce0a75d3a93
@@ -1664,7 +1664,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d65d1f297ddb07b799ff5b2e560575fc59a6fa74c752269cc85ab84348fb7da4
-R 49fa7e54acb9ad8a392e6c25fe8116d5
-U mistachkin
-Z 3270bf7f35234fd560a264ffe40cbf35
+P ac8786f3f9f35cb6fa72c65f5ca41cc6659f4702cd29ab0c9dcf04d3d1189090
+R 88b26813bcaf999746e4cf55503b4797
+U drh
+Z fe6d8478e3f31cb2dfbec6ce858d4ad8
diff --git a/manifest.uuid b/manifest.uuid
index 63b3b0cf2b..12179a84a0 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-ac8786f3f9f35cb6fa72c65f5ca41cc6659f4702cd29ab0c9dcf04d3d1189090
\ No newline at end of file
+ee31c04353cd75ea4bbadee2994c30d3808b696a4f680187502d104902988a5d
\ No newline at end of file
diff --git a/src/where.c b/src/where.c
index 5a3d44f9ee..95bbdb157e 100644
--- a/src/where.c
+++ b/src/where.c
@@ -1885,16 +1885,15 @@ static void whereInfoFree(sqlite3 *db, WhereInfo *pWInfo){
 ** Return TRUE if all of the following are true:
 **
 **   (1)  X has the same or lower cost that Y
-**   (2)  X is a proper subset of Y
-**   (3)  X skips at least as many columns as Y
-**
-** By "proper subset" we mean that X uses fewer WHERE clause terms
-** than Y and that every WHERE clause term used by X is also used
-** by Y.
+**   (2)  X users fewer WHERE clause terms than Y
+**   (3)  Every WHERE clause term used by X is also used by Y
+**   (4)  X skips at least as many columns as Y
+**   (5)  If X is a covering index, than Y is too
 **
+** Conditions (2) and (3) mean that X is a "proper subset" of Y.
 ** If X is a proper subset of Y then Y is a better choice and ought
 ** to have a lower cost.  This routine returns TRUE when that cost 
-** relationship is inverted and needs to be adjusted.  The third rule
+** relationship is inverted and needs to be adjusted.  Constraint (4)
 ** was added because if X uses skip-scan less than Y it still might
 ** deserve a lower cost even if it is a proper subset of Y.
 */
@@ -1918,6 +1917,10 @@ static int whereLoopCheaperProperSubset(
     }
     if( j<0 ) return 0;  /* X not a subset of Y since term X[i] not used by Y */
   }
+  if( (pX->wsFlags&WHERE_IDX_ONLY)!=0 
+   && (pY->wsFlags&WHERE_IDX_ONLY)==0 ){
+    return 0;  /* Constraint (5) */
+  }
   return 1;  /* All conditions meet */
 }
 
diff --git a/test/analyze9.test b/test/analyze9.test
index 918577bd19..7c69806f89 100644
--- a/test/analyze9.test
+++ b/test/analyze9.test
@@ -1052,8 +1052,11 @@ do_execsql_test 23.0 {
 do_eqp_test 23.1 {
   SELECT * FROM t4 WHERE 
     (e=1 AND b='xyz' AND c='zyx' AND a<'AEA') AND f<300
+  -- Formerly used index i41.  But i41 is not a covering index whereas
+  -- the PRIMARY KEY is a covering index, and so as of 2017-10-15, the
+  -- PRIMARY KEY is preferred.
 } {
-  0 0 0 {SEARCH TABLE t4 USING INDEX i41 (e=? AND c=? AND b=? AND a<?)}
+  0 0 0 {SEARCH TABLE t4 USING PRIMARY KEY (c=? AND b=? AND a<?)}
 }
 do_eqp_test 23.2 {
   SELECT * FROM t4 WHERE