diff --git a/interpolation/cspline.c b/interpolation/cspline.c
index e6a1abc..37c73d4 100644
--- a/interpolation/cspline.c
+++ b/interpolation/cspline.c
@@ -334,7 +334,7 @@ cspline_eval_deriv (const void * vstate,
   else
     {
       *dydx = 0.0;
-      return GSL_FAILURE;
+      return GSL_EINVAL;
     }
 }
 
@@ -380,7 +380,7 @@ cspline_eval_deriv2 (const void * vstate,
   else
     {
       *y_pp = 0.0;
-      return GSL_FAILURE;
+      return GSL_EINVAL;
     }
 }
 
@@ -435,7 +435,7 @@ cspline_eval_integ (const void * vstate,
     }
     else {
       *result = 0.0;
-      return GSL_FAILURE;
+      return GSL_EINVAL;
     }
   }