Index: src/expr.c
==================================================================
--- src/expr.c
+++ src/expr.c
@@ -4944,10 +4944,11 @@
     return 1;
   }
   if( pE2->op==TK_NOTNULL
    && pE1->op!=TK_ISNULL
    && pE1->op!=TK_IS
+   && pE1->op!=TK_ISNOT
    && pE1->op!=TK_OR
   ){
     Expr *pX = sqlite3ExprSkipCollate(pE1->pLeft);
     testcase( pX!=pE1->pLeft );
     if( sqlite3ExprCompare(pParse, pX, pE2->pLeft, iTab)==0 ) return 1;

Index: test/index6.test
==================================================================
--- test/index6.test
+++ test/index6.test
@@ -420,7 +420,18 @@
   CREATE TABLE t0(c0);
   CREATE INDEX index_0 ON t0(c0) WHERE c0 NOT NULL;
   INSERT INTO t0(c0) VALUES (NULL);
   SELECT * FROM t0 WHERE c0 OR 1;
 } {{}}
+
+# 2019-05-11
+# Ticket https://sqlite.org/src/tktview/8025674847
+reset_db
+do_execsql_test index6-14.1 {
+  CREATE TABLE IF NOT EXISTS t0 (c0, c1);
+  CREATE INDEX IF NOT EXISTS i0 ON t0(c0, c1) WHERE c0 NOT NULL;
+  INSERT INTO t0(c0, c1) VALUES(NULL, 'row');
+  SELECT * FROM t0 WHERE t0.c0 IS NOT 1;
+} {{} row}
 
 finish_test
+