diff --git a/libm65/decode1a.f b/libm65/decode1a.f
index 96831ad5c..0a6d8bc75 100644
--- a/libm65/decode1a.f
+++ b/libm65/decode1a.f
@@ -1,6 +1,6 @@
       subroutine decode1a(dd,newdat,f0,nflip,mode65,nfsample,xpol,
      +  mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,ndphi,iloop,
-     +  nutc,nkhz,ndf,ipol,sync2,a,dt,pol,nkv,nhist,nsum,nsave,
+     +  nutc,nkhz,ndf,ipol,ntol,sync2,a,dt,pol,nkv,nhist,nsum,nsave,
      +  qual,decoded)
 
 !  Apply AFC corrections to a candidate JT65 signal, then decode it.
@@ -134,14 +134,15 @@
 
       if(nqd.eq.1 .and. nkv.eq.0) then
          nhz=1000*nkhz + ndf
-         if(nutc.ne.nutc0 .or. abs(nhz-nhz0).ge.1000) syncbest=0.   !### 1000 ??
+         ihzdiff=min(500,ntol)
+         if(nutc.ne.nutc0 .or. abs(nhz-nhz0).ge.ihzdiff) syncbest=0.
          if(sync2.gt.syncbest) then
             nsave=nsave+1
             nsave=mod(nsave-1,64)+1
             npol=nint(57.296*pol)
             xdt=dt+0.8
 
-            call s3avg(nsave,mode65,nutc,nhz,xdt,npol,s3,nsum,
+            call s3avg(nsave,mode65,nutc,nhz,xdt,npol,ntol,s3,nsum,
      +                 nkv,decoded)
             syncbest=sync2
             nhz0=nhz
diff --git a/libm65/map65a.f90 b/libm65/map65a.f90
index 38ebd7745..21694d4a5 100644
--- a/libm65/map65a.f90
+++ b/libm65/map65a.f90
@@ -206,8 +206,8 @@ subroutine map65a(dd,ss,savg,newdat,nutc,fcenter,ntol,idphi,nfa,nfb,        &
                  idf=nint(1000.0*(freq+0.5*(nfa+nfb)-foffset-(ikHz+nfshift)))
                  call decode1a(dd,newdat,f00,nflip,mode65,nfsample,xpol,  &
                       mycall,hiscall,hisgrid,neme,ndepth,nqd,dphi,ndphi,  &
-                      iloop,nutc,ikHz,idf,ipol,sync2,a,dt,pol,nkv,nhist,  &
-                      nsum,nsave,qual,decoded)
+                      iloop,nutc,ikHz,idf,ipol,ntol,sync2,a,dt,pol,nkv,   &
+                      nhist,nsum,nsave,qual,decoded)
                  dt=dt+0.8                           !### empirical tweak
                  call timer('decode1a',1)
 
diff --git a/libm65/s3avg.f90 b/libm65/s3avg.f90
index 437286bef..555572464 100644
--- a/libm65/s3avg.f90
+++ b/libm65/s3avg.f90
@@ -1,4 +1,4 @@
-subroutine s3avg(nsave,mode65,nutc,nhz,xdt,npol,s3,nsum,nkv,decoded)
+subroutine s3avg(nsave,mode65,nutc,nhz,xdt,npol,ntol,s3,nsum,nkv,decoded)
 
 ! Save the current synchronized spectra, s3(64,63), for possible
 ! decoding of average.
@@ -18,7 +18,7 @@ subroutine s3avg(nsave,mode65,nutc,nhz,xdt,npol,s3,nsum,nkv,decoded)
      ihz=0
      ipol=0
      first=.false.
-     ihzdiff=100
+     ihzdiff=min(100,ntol)
      dtdiff=0.2
   endif
 
diff --git a/mainwindow.cpp b/mainwindow.cpp
index 7f0050f2f..1bdab40ba 100644
--- a/mainwindow.cpp
+++ b/mainwindow.cpp
@@ -1,4 +1,4 @@
-//-------------------------------------------------------------- MainWindow
+//--------------------------------------------------------------- MainWindow
 #include "mainwindow.h"
 #include "ui_mainwindow.h"
 #include "devsetup.h"