diff --git a/lib/fchisq65.f90 b/lib/fchisq65.f90
index 4231dead1..fbfc4a265 100644
--- a/lib/fchisq65.f90
+++ b/lib/fchisq65.f90
@@ -45,7 +45,7 @@ real function fchisq65(cx,npts,fsample,nflip,a,ccfmax,dtmax)
      j=nsps+(i-1)*nsps/16 !steps by 8 samples (1/16 of a symbol)
      k=j-nsps
      ss(i)=0.
-     if(k.ge.0) then
+     if(k.ge.0 .and. j.le.npts) then
         z=csx(j)-csx(k) ! difference over span of 128 pts
         ss(i)=fac*(real(z)**2 + aimag(z)**2)
      endif
diff --git a/lib/jt65sim.f90 b/lib/jt65sim.f90
index 4afd03cf6..b9d8c3979 100644
--- a/lib/jt65sim.f90
+++ b/lib/jt65sim.f90
@@ -111,7 +111,7 @@ program jt65sim
         k=12000 + xdt*12000                 !Start audio at t = xdt + 1.0 s
         isym0=-99
         do i=1,npts                         !Add this signal into cdat()
-           isym=nint(i/sps)+1
+           isym=floor(i/sps)+1
            if(isym.gt.nsym) exit
            if(isym.ne.isym0) then
               freq=f0 + itone(isym)*baud*mode65