Index: src/vdbe.c
==================================================================
--- src/vdbe.c
+++ src/vdbe.c
@@ -1721,38 +1721,32 @@
   sqlite3VdbeMemIntegerify(pIn1);
   pIn1->u.i += pOp->p2;
   break;
 }
 
-/* Opcode: MustBeInt P1 P2 * * P5
+/* Opcode: MustBeInt P1 P2 * * *
 ** 
-** If P5 is 0, force the value in register P1 to be an integer. If 
-** the value in P1 is not an integer and cannot be converted into an 
-** integer without data loss, then jump immediately to P2, or if P2==0
+** Force the value in register P1 to be an integer.  If the value
+** in P1 is not an integer and cannot be converted into an integer
+** without data loss, then jump immediately to P2, or if P2==0
 ** raise an SQLITE_MISMATCH exception.
-**
-** Or, if P5 is non-zero, then force the register in P1 to be a number
-** (real or integer). Jump to P2 if this cannot be accomplished without
-** data loss. P2 must be non-zero in this case.
 */
 case OP_MustBeInt: {            /* jump, in1 */
-  u8 f;
-  f = (pOp->p5 ? (MEM_Int|MEM_Real) : MEM_Int);
   pIn1 = &aMem[pOp->p1];
-  if( (pIn1->flags & f)==0 ){
+  if( (pIn1->flags & MEM_Int)==0 ){
     applyAffinity(pIn1, SQLITE_AFF_NUMERIC, encoding);
-    VdbeBranchTaken((pIn1->flags&f)==0, 2);
-    if( (pIn1->flags & f)==0 ){
+    VdbeBranchTaken((pIn1->flags&MEM_Int)==0, 2);
+    if( (pIn1->flags & MEM_Int)==0 ){
       if( pOp->p2==0 ){
         rc = SQLITE_MISMATCH;
         goto abort_due_to_error;
       }else{
         goto jump_to_p2;
       }
     }
   }
-  if( f==MEM_Int ) MemSetTypeFlag(pIn1, MEM_Int);
+  MemSetTypeFlag(pIn1, MEM_Int);
   break;
 }
 
 #ifndef SQLITE_OMIT_FLOATING_POINT
 /* Opcode: RealAffinity P1 * * * *

Index: src/window.c
==================================================================
--- src/window.c
+++ src/window.c
@@ -1300,12 +1300,18 @@
   static int aOp[] = { OP_Ge, OP_Ge, OP_Gt, OP_Ge, OP_Ge };
   Vdbe *v = sqlite3GetVdbe(pParse);
   int regZero = sqlite3GetTempReg(pParse);
   assert( eCond>=0 && eCond<ArraySize(azErr) );
   sqlite3VdbeAddOp2(v, OP_Integer, 0, regZero);
-  sqlite3VdbeAddOp2(v, OP_MustBeInt, reg, sqlite3VdbeCurrentAddr(v)+2);
-  if( eCond>=WINDOW_STARTING_NUM ) sqlite3VdbeChangeP5(v, 1);
+  if( eCond>=WINDOW_STARTING_NUM ){
+    int regString = sqlite3GetTempReg(pParse);
+    sqlite3VdbeAddOp4(v, OP_String8, 0, regString, 0, "", P4_STATIC);
+    sqlite3VdbeAddOp3(v, OP_Ge, regString, sqlite3VdbeCurrentAddr(v)+2, reg);
+    sqlite3VdbeChangeP5(v, SQLITE_AFF_NUMERIC);
+  }else{
+    sqlite3VdbeAddOp2(v, OP_MustBeInt, reg, sqlite3VdbeCurrentAddr(v)+2);
+  }
   VdbeCoverageIf(v, eCond==0);
   VdbeCoverageIf(v, eCond==1);
   VdbeCoverageIf(v, eCond==2);
   sqlite3VdbeAddOp3(v, aOp[eCond], regZero, sqlite3VdbeCurrentAddr(v)+2, reg);
   VdbeCoverageNeverNullIf(v, eCond==0);

Index: test/window1.test
==================================================================
--- test/window1.test
+++ test/window1.test
@@ -935,9 +935,41 @@
   SELECT
     current, exclude, filter, following, groups, no, others, over,
     partition, preceding, range, ties, unbounded, window
   FROM keyword_tab
 }
+
+#-------------------------------------------------------------------------
+foreach {tn expr err} {
+  1   4.5      0
+  2   NULL     1
+  3   0.0      0
+  4   0.1      0
+  5  -0.1      1
+  6  ''        1
+  7  '2.0'     0
+  8  '2.0x'    1
+  9  x'1234'   1
+ 10  '1.2'     0
+} {
+  set res {0 1}
+  if {$err} {set res {1 {frame starting offset must be a non-negative number}} }
+  do_catchsql_test 22.$tn.1 "
+    WITH a(x, y) AS ( VALUES(1, 2) )
+    SELECT sum(x) OVER (
+      ORDER BY y RANGE BETWEEN $expr PRECEDING AND UNBOUNDED FOLLOWING
+    ) FROM a
+  " $res
+
+  set res {0 1}
+  if {$err} {set res {1 {frame ending offset must be a non-negative number}} }
+  do_catchsql_test 22.$tn.2 "
+    WITH a(x, y) AS ( VALUES(1, 2) )
+    SELECT sum(x) OVER (
+      ORDER BY y RANGE BETWEEN UNBOUNDED PRECEDING AND $expr FOLLOWING
+    ) FROM a
+  " $res
+}
 
 finish_test