diff --git a/lib/sync4.f90 b/lib/sync4.f90
index a15177665..e3a6a24de 100644
--- a/lib/sync4.f90
+++ b/lib/sync4.f90
@@ -140,8 +140,9 @@ subroutine sync4(dat,jz,ntol,nfqso,mode,mode4,minwidth,dtx,dfx,snrx,    &
      endif
   enddo
   rms=0.1
+  snrx=-26.0
   if(ns.gt.0) rms=sqrt(sq/ns)
-  snrx=10.0*log10(ccfred(ipk1a)/rms) - 41.2
+  if(ccfred(ipk1a).gt.0.0) snrx=10.0*log10(ccfred(ipk1a)/rms) - 41.2
   if(snrx.gt.50.0) snrx=50.0
 
 900  return