Index: src/expr.c
==================================================================
--- src/expr.c
+++ src/expr.c
@@ -3122,17 +3122,22 @@
     CollSeq *pColl = sqlite3ExprCollSeq(pParse, pExpr->pLeft);
     int labelOk = sqlite3VdbeMakeLabel(pParse);
     int r2, regToFree;
     int regCkNull = 0;
     int ii;
+    int bLhsReal;  /* True if the LHS of the IN has REAL affinity */
     assert( !ExprHasProperty(pExpr, EP_xIsSelect) );
     if( destIfNull!=destIfFalse ){
       regCkNull = sqlite3GetTempReg(pParse);
       sqlite3VdbeAddOp3(v, OP_BitAnd, rLhs, rLhs, regCkNull);
     }
+    bLhsReal = sqlite3ExprAffinity(pExpr->pLeft)==SQLITE_AFF_REAL;
     for(ii=0; ii<pList->nExpr; ii++){
       r2 = sqlite3ExprCodeTemp(pParse, pList->a[ii].pExpr, &regToFree);
+      if( bLhsReal ){
+        sqlite3VdbeAddOp4(v, OP_Affinity, r2, 1, 0, "E", P4_STATIC);
+      }
       if( regCkNull && sqlite3ExprCanBeNull(pList->a[ii].pExpr) ){
         sqlite3VdbeAddOp3(v, OP_BitAnd, regCkNull, r2, regCkNull);
       }
       if( ii<pList->nExpr-1 || destIfNull!=destIfFalse ){
         sqlite3VdbeAddOp4(v, OP_Eq, rLhs, labelOk, r2,

Index: test/in.test
==================================================================
--- test/in.test
+++ test/in.test
@@ -757,7 +757,23 @@
   CREATE TABLE t0(c0 INT UNIQUE);
   INSERT INTO t0(c0) VALUES (1);
   SELECT * FROM t0 WHERE '1' IN (t0.c0);
 } {}
 
+# 2019-09-02 ticket https://www.sqlite.org/src/info/2841e99d104c6436
+# For the IN_INDEX_NOOP optimization, apply REAL affinity to the LHS
+# values prior to comparison if the RHS has REAL affinity.
+#
+do_execsql_test in-19.1 {
+  DROP TABLE IF EXISTS t0;
+  CREATE TABLE t0(c0 REAL UNIQUE);
+  INSERT INTO t0(c0) VALUES(2.07093491255203046E18);
+  SELECT 1 FROM t0 WHERE c0 IN ('2070934912552030444');
+} {1}
+do_execsql_test in-19.2 {
+  SELECT c0 IN ('2070934912552030444') FROM t0;
+} {1}
+do_execsql_test in-19.3 {
+  SELECT c0 IN ('2070934912552030444',2,3) FROM t0;
+} {1}
 
 finish_test