diff --git a/lib/ft4/ft4_downsample.f90 b/lib/ft4/ft4_downsample.f90
index 819b10fbc..d3760a506 100644
--- a/lib/ft4/ft4_downsample.f90
+++ b/lib/ft4/ft4_downsample.f90
@@ -38,7 +38,7 @@ subroutine ft4_downsample(dd,newdata,f0,c)
    endif
    i0=nint(f0/df)
    c1=0.
-   c1(0)=cx(i0)
+   if(i0.ge.0 .and. i0.le.NMAX/2) c1(0)=cx(i0)
    do i=1,NFFT2/2
       if(i0+i.le.NMAX/2) c1(i)=cx(i0+i)
       if(i0-i.ge.0) c1(NFFT2-i)=cx(i0-i)
diff --git a/lib/ft4/getcandidates4.f90 b/lib/ft4/getcandidates4.f90
index 5d42ca740..badbbcfb5 100644
--- a/lib/ft4/getcandidates4.f90
+++ b/lib/ft4/getcandidates4.f90
@@ -69,6 +69,7 @@ subroutine getcandidates4(dd,fa,fb,syncmin,nfqso,maxcand,savg,candidate,   &
         del=0.
         if(den.ne.0.0)  del=0.5*(savsm(i-1)-savsm(i+1))/den
         fpeak=(i+del)*df+f_offset
+        if(fpeak.lt.0.0 .or. fpeak.gt.4910.0) cycle
         speak=savsm(i) - 0.25*(savsm(i-1)-savsm(i+1))*del
         ncand=ncand+1
         if(ncand.gt.maxcand) then