Index: src/where.c
==================================================================
--- src/where.c
+++ src/where.c
@@ -3860,10 +3860,13 @@
           if( iColumn==XN_ROWID ){
             testcase( distinctColumns==0 );
             distinctColumns = 1;
           }
           obSat |= MASKBIT(i);
+          if( (wctrlFlags & WHERE_ORDERBY_MIN) && j==pLoop->u.btree.nEq ){
+            pLoop->wsFlags |= WHERE_MIN_ORDERED;
+          }
         }else{
           /* No match found */
           if( j==0 || j<nKeyCol ){
             testcase( isOrderDistinct!=0 );
             isOrderDistinct = 0;

Index: src/whereInt.h
==================================================================
--- src/whereInt.h
+++ src/whereInt.h
@@ -584,7 +584,8 @@
 #define WHERE_AUTO_INDEX   0x00004000  /* Uses an ephemeral index */
 #define WHERE_SKIPSCAN     0x00008000  /* Uses the skip-scan algorithm */
 #define WHERE_UNQ_WANTED   0x00010000  /* WHERE_ONEROW would have been helpful*/
 #define WHERE_PARTIALIDX   0x00020000  /* The automatic index is partial */
 #define WHERE_IN_EARLYOUT  0x00040000  /* Perhaps quit IN loops early */
+#define WHERE_MIN_ORDERED  0x00080000  /* Column nEq of index is min() expr */
 
 #endif /* !defined(SQLITE_WHEREINT_H) */

Index: src/wherecode.c
==================================================================
--- src/wherecode.c
+++ src/wherecode.c
@@ -1560,17 +1560,16 @@
     ** a single iteration. This means that the first row returned
     ** should not have a NULL value stored in 'x'. If column 'x' is
     ** the first one after the nEq equality constraints in the index,
     ** this requires some special handling.
     */
-    assert( pWInfo->pOrderBy==0
-         || pWInfo->pOrderBy->nExpr==1
+    assert( (pWInfo->pOrderBy!=0 && pWInfo->pOrderBy->nExpr==1)
          || (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)==0 );
-    if( (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN)!=0
-     && pWInfo->nOBSat>0
-     && (pIdx->nKeyCol>nEq)
-    ){
+    if( pLoop->wsFlags & WHERE_MIN_ORDERED ){
+      assert( (pWInfo->wctrlFlags&WHERE_ORDERBY_MIN) );
+      assert( pWInfo->nOBSat );
+      assert( pIdx->nColumn>nEq );
       assert( pLoop->nSkip==0 );
       bSeekPastNull = 1;
       nExtraReg = 1;
     }
 

Index: test/minmax4.test
==================================================================
--- test/minmax4.test
+++ test/minmax4.test
@@ -175,7 +175,30 @@
   } {2 2}
   do_execsql_test 3.$tn.5 {
     SELECT min(a), b FROM t1 WHERE a<50;
   } {2 2}
 }
+
+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 4.0 {
+  CREATE TABLE t0 (c0, c1);
+  CREATE INDEX i0 ON t0(c1, c1 + 1 DESC);
+  INSERT INTO t0(c0) VALUES (1);
+}
+do_execsql_test 4.1 {
+  SELECT MIN(t0.c1), t0.c0 FROM t0 WHERE t0.c1 ISNULL; 
+} {{} 1}
+
+#-------------------------------------------------------------------------
+reset_db
+do_execsql_test 5.0 {
+  CREATE TABLE t1 (a, b);
+  INSERT INTO t1 VALUES(123, NULL);
+  CREATE INDEX i1 ON t1(a, b DESC);
+}
+do_execsql_test 5.1 {
+  SELECT MIN(a) FROM t1 WHERE a=123;
+} {123}
 
 finish_test
+