diff --git a/lib/fst280_decode.f90 b/lib/fst280_decode.f90
index 8896af544..a5b84d681 100644
--- a/lib/fst280_decode.f90
+++ b/lib/fst280_decode.f90
@@ -159,7 +159,7 @@ contains
       do isync=0,1
          if(isync.eq.0) then
             fc1=0.0
-            is0=nint(fs2)
+            is0=2*nint(fs2)
             ishw=is0
             isst=4
             ifhw=10