diff --git a/fil651.f b/fil651.f
index 90d3509ba..7f633d91c 100644
--- a/fil651.f
+++ b/fil651.f
@@ -16,7 +16,7 @@ C  fout        = 2706.25  Hz
       parameter (NDOWN=2)               !Downsample ratio
 
       real d(n1)
-      complex c(*)
+      complex c(n2)
 
       complex ck(-NH:NH)
       data ck/
diff --git a/fil652.f b/fil652.f
index 90aafc15a..ac0d26dba 100644
--- a/fil652.f
+++ b/fil652.f
@@ -14,7 +14,7 @@ C  fout        = 1378.125 Hz
       parameter (NH=NTAPS/2)
       parameter (NDOWN=2)                !Downsample ratio
       complex c1(n1)
-      complex c2(*)
+      complex c2(n2)
 
 C  Filter coefficients:
       real a(-NH:NH)
diff --git a/fil653.f b/fil653.f
index b97b1fa77..aa60ba026 100644
--- a/fil653.f
+++ b/fil653.f
@@ -15,7 +15,7 @@ C  BW          = 200        Hz
       parameter (NH=NTAPS/2)
       parameter (NDOWN=4)                !Downsample ratio
       complex c1(n1)
-      complex c2(*)
+      complex c2(n2)
 
 C  Filter coefficients:
       real a(-NH:NH)
diff --git a/ftpeak65.f b/ftpeak65.f
index bdd3cbe93..29d0bdd5b 100644
--- a/ftpeak65.f
+++ b/ftpeak65.f
@@ -22,6 +22,7 @@ C  compute ftrack.
       twopi=8*datan(1.d0)
       fsyncset=-300.d0
       dt=2.d0/11025.d0               !Input dt (WSJT has downsampled by 2)
+      n2 = NMAX/2
       call fil651(dat,jz,c2,n2)      !Filter and complex mix; rate 1/2
       dt=2.d0*dt                     !We're now downsampled by 4
 
@@ -32,6 +33,7 @@ C  compute ftrack.
          c2(i)=c2(i) * cmplx(cos(pha),-sin(pha))
       enddo
 
+      n3 = NMAX/4
       call fil652(c2,n2,c3,n3)       !Low-pass at +/- 500 Hz; rate 1/2
       dt=2.d0*dt                     !Down by 8
 
@@ -42,9 +44,11 @@ C  compute ftrack.
          c3(i)=c3(i) * cmplx(cos(pha),-sin(pha))
       enddo
 
+      n4 = NMAX/16
       call fil653(c3,n3,c4,n4)       !Low-pass at +/- 100 Hz; rate 1/4
       dt=4.d0*dt                     !Down by 32
 
+      n5 = NMAX/64
       call fil653(c4,n4,c5,n5)       !Low-pass at +/- 25 Hz; rate 1/4
       dt=4.d0*dt                     !Down by 128