diff --git a/lib/jt65_decode.f90 b/lib/jt65_decode.f90
index 8ac539e94..4e73ee7b1 100644
--- a/lib/jt65_decode.f90
+++ b/lib/jt65_decode.f90
@@ -162,6 +162,7 @@ contains
           ib=min(NSZ,nint((nfb+100)/df))
           nz=ib-ia+1
           if(nz.lt.50) go to 900
+          if(isnan(sum(savg(ia:ia+nz-1)))) go to 900
           call lorentzian(savg(ia),nz,a)
           baseline=a(1)
           amp=a(2)