diff --git a/src/swiftest/swiftest_drift.f90 b/src/swiftest/swiftest_drift.f90
index fe315fc74..0fdb0f63f 100644
--- a/src/swiftest/swiftest_drift.f90
+++ b/src/swiftest/swiftest_drift.f90
@@ -207,6 +207,12 @@ pure subroutine swiftest_drift_dan(mu, rx0, ry0, rz0, vx0, vy0, vz0, dt0, iflag)
          end if
       end if
 
+      ! For debugging overflow error
+
+      if(r0 .ge. 11970204779.00) then
+         f = 1.0_DP
+      end if
+
       call swiftest_drift_kepu(dt, r0, mu, alpha, u, fp, c1, c2, c3, iflag)
       if (iflag == 0) then
          f = 1.0_DP - mu / r0 * c2
@@ -462,10 +468,10 @@ pure subroutine swiftest_drift_kepu_new(s, dt, r0, mu, alpha, u, fp, c1, c2, c3,
          x = s*s*alpha
 
          ! for debugging overflow error
-         if (abs(x) .ge. HUGE(0.0_DP)) then
-            write(*,*) "big x"
+         if (abs(x) .ge. HUGE(0.0_DP) .or. x < 0) then
+            f = 1.0_DP ! "big x"
          end if 
-         
+
          call swiftest_drift_kepu_stumpff(x, c0, c1, c2, c3)
          c1 = c1*s
          c2 = c2*s*s
@@ -559,28 +565,12 @@ pure subroutine swiftest_drift_kepu_stumpff(x, c0, c1, c2, c3)
       integer(I4B) :: i, n
       real(DP)   :: xm
 
-
-      ! for debugging Floating overflow error
-      if (abs(x) .ge. HUGE(0.0_DP)) then
-         write(*,*) "big x"
-      end if
-
-      if (abs(c0) .ge. HUGE(0.0_DP)) then
-         write(*,*) "big c0"
-      end if
-
-      if (abs(c1) .ge. HUGE(0.0_DP)) then
-         write(*,*) "big c1"
-      end if
-
-      if (abs(c2) .ge. HUGE(0.0_DP)) then
-         write(*,*) "big c2"
-      end if
-
-      if (abs(c3) .ge. HUGE(0.0_DP)) then
-         write(*,*) "big c3"
+      ! for debugging overflow error
+      if (abs(x) .ge. HUGE(0.0_DP) .or. x < 0) then
+         x = x ! "big x"
+         n = 0
       end if
-
+      
       n = 0
       xm = 0.1_DP
       do while (abs(x) >= xm)
@@ -605,6 +595,25 @@ pure subroutine swiftest_drift_kepu_stumpff(x, c0, c1, c2, c3)
          end do
       end if
 
+      ! for debugging Floating overflow error
+
+      if (abs(c0) .ge. HUGE(0.0_DP)) then
+         xm = 0.1_DP ! "big c0"
+      end if
+
+      if (abs(c1) .ge. HUGE(0.0_DP)) then
+         xm = 0.1_DP ! "big c1"
+      end if
+
+      if (abs(c2) .ge. HUGE(0.0_DP)) then
+         xm = 0.1_DP ! "big c2"
+      end if
+
+      if (abs(c3) .ge. HUGE(0.0_DP)) then
+         xm = 0.1_DP ! "big c3"
+      end if
+
+
       return
    end subroutine swiftest_drift_kepu_stumpff