--- cvs/gsl/ode-initval/evolve.c	2007-12-14 23:53:49.000000000 +0100
+++ cvs-no-ode-bug/gsl/ode-initval/evolve.c	2007-12-26 22:51:34.000000000 +0100
@@ -199,15 +199,28 @@
   if (con != NULL)
     {
       /* Check error and attempt to adjust the step. */
+      const double h0_old = h0;
       const int hadjust_status 
         = gsl_odeiv_control_hadjust (con, step, y, e->yerr, e->dydt_out, &h0);
 
       if (hadjust_status == GSL_ODEIV_HADJ_DEC)
         {
-          /* Step was decreased. Undo and go back to try again. */
-          DBL_MEMCPY (y, e->y0, dydt->dimension);
-          e->failed_steps++;
-          goto try_step;
+	  /* Step size h0 was decreased. Make sure it does not get too small:
+	     It should be positive (i.e., h0 >= GSL_DBL_MIN) and not 
+	     smaller than GSL_DBL_EPSILON * t0 (because t0 + h0 has to be 
+	     distinguishable from t0) */
+
+	  h0 = GSL_MAX_DBL (h0, GSL_MAX_DBL (GSL_DBL_MIN, GSL_DBL_EPSILON * t0));
+
+          /* If the step size h0 is still smaller than in the previous step, 
+	     undo and go back to try again. */
+
+	  if (h0 < h0_old) 
+	    {
+	      DBL_MEMCPY (y, e->y0, dydt->dimension);
+	      e->failed_steps++;
+	      goto try_step;
+	    }
         }
     }