diff --git a/src/dierckx.f90 b/src/dierckx.f90
index 4ee9771..d339d17 100644
--- a/src/dierckx.f90
+++ b/src/dierckx.f90
@@ -1762,6 +1762,7 @@ contains
   subroutine fpgrre(ifsx,ifsy,ifbx,ifby,x,mx,y,my,z,mz,kx,ky,tx,nx, &
      ty,ny,p,c,nc,fp,fpx,fpy,mm,mynx,kx1,kx2,ky1,ky2,spx,spy,right,q, &
      ax,ay,bx,by,nrx,nry)
+    use, intrinsic :: ieee_arithmetic, only : ieee_is_finite
 !  ..
 ! arguments
     integer, intent(in) :: kx, kx1, kx2, ky, ky1, ky2, mm, mx, my, mz, &
@@ -2087,6 +2088,7 @@ contains
         term = (z(iz)-term)**2
 !  adjust the different parameters.
         fp = fp+term
+        if (.not. ieee_is_finite(fp)) exit
         fpx(numx1) = fpx(numx1)+term
         fpy(numy1) = fpy(numy1)+term
         fac = term*half