diff --git a/lib/detectmsk40.f90 b/lib/detectmsk40.f90
index fe8d9194e..68b4abef7 100644
--- a/lib/detectmsk40.f90
+++ b/lib/detectmsk40.f90
@@ -205,10 +205,22 @@ subroutine detectmsk40(cbig,n,pchk_file,mycall,hiscall,lines,nmessages,   &
     t0=times(ip) + t00
     cdat=cbig(imid-NPTS/2+1:imid+NPTS/2)
     ferr=ferrs(ip)
-    nsnr=nint(snrs(ip))
     xsnr=snrs(ip)
-    if( nsnr .lt. -5 ) nsnr=-5
-    if( nsnr .gt. 25 ) nsnr=25
+    if( xsnr .lt. -1.5 ) then
+      nsnr=-3
+    else if( xsnr .lt. 1.5 ) then
+      nsnr=0
+    else if( xsnr .lt. 4.5 ) then
+      nsnr=3
+    else if( xsnr .lt. 8.0 ) then
+      nsnr=6 
+    else if( xsnr .lt. 11.5 ) then
+      nsnr=10 
+    else if( xsnr .lt. 14.5 ) then
+      nsnr=13 
+    else 
+      nsnr=16 
+    endif
 
 ! remove coarse freq error
     call tweak1(cdat,NPTS,-(1500+ferr),cdat)