diff --git a/lib/sync4.f90 b/lib/sync4.f90
index 9bfe6c60b..3d2974f64 100644
--- a/lib/sync4.f90
+++ b/lib/sync4.f90
@@ -85,7 +85,7 @@ subroutine sync4(dat,jz,ntol,nfqso,mode,mode4,minwidth,dtx,dfx,snrx,    &
   enddo
   if(syncbest.lt.-1.e29) go to 900
   ccfred=red
-  call pctile(ccfred(iaa:ibb),ibb-iaa+1,45,base)
+  call pctile(ccfred(ia:ib),ib-ia+1,45,base)
   ccfred=ccfred-base
   
   dfx=ipk*df