diff --git a/compiler/jsgen.nim b/compiler/jsgen.nim
index 4fde4e300ce3b..1b34a6564197f 100644
--- a/compiler/jsgen.nim
+++ b/compiler/jsgen.nim
@@ -606,12 +606,12 @@ proc arithAux(p: PProc, n: PNode, r: var TCompRes, op: TMagic) =
     if n[1].typ.size <= 4:
       applyFormat("($1 << $2)", "($1 << $2)")
     else:
-      applyFormat("($1 * Math.pow(2,$2))", "($1 * Math.pow(2,$2))")
+      applyFormat("mulInt($1, Math.pow(2,$2))", "($1 * Math.pow(2,$2))")
   of mAshrI: 
     if n[1].typ.size <= 4:
       applyFormat("($1 >> $2)", "($1 >> $2)")
     else:
-      applyFormat("Math.floor($1 / Math.pow(2,$2))", "Math.floor($1 / Math.pow(2,$2))")
+      applyFormat("divInt($1, Math.pow(2,$2))", "Math.trunc($1 / Math.pow(2,$2))")
   of mBitandI: applyFormat("($1 & $2)", "($1 & $2)")
   of mBitorI: applyFormat("($1 | $2)", "($1 | $2)")
   of mBitxorI: applyFormat("($1 ^ $2)", "($1 ^ $2)")