diff --git a/src/scgenerator/solver.py b/src/scgenerator/solver.py
index f10c951..f443aa3 100644
--- a/src/scgenerator/solver.py
+++ b/src/scgenerator/solver.py
@@ -2,6 +2,7 @@ from __future__ import annotations
 
 import json
 import os
+import sys
 import warnings
 import zipfile
 from collections import defaultdict
@@ -227,7 +228,10 @@ def solve43(
                 continue
         else:
             rejected.append((h, error))
-            print(f"{z = :.3f} rejected step {step_ind} with {h = :.2g}, {error = :.2g}")
+            print(
+                f"{z = :.3f} rejected step {step_ind} with {h = :.2g}, {error = :.2g}",
+                file=sys.stderr,
+            )
 
         h = h * next_h_factor
 
@@ -238,7 +242,7 @@ def solve43(
             store_next = False
 
         if msg.ready():
-            print(f"step {step_ind}, {z = :.3f}, {error = :g}, {h = :.3g}")
+            print(f"step {step_ind}, {z = :.3f}, {error = :g}, {h = :.3g}", file=sys.stderr)
 
 
 def integrate(
@@ -261,7 +265,7 @@ def integrate(
             solve43(spec0, linear, nonlinear, length, atol, rtol, safety, targets=targets)
         ):
             if msg.ready():
-                print(f"step {i}, z = {new_stat['z']*100:.2f}cm")
+                print(f"step {i}, z = {new_stat['z']*100:.2f}cm", file=sys.stderr)
             all_spectra.append(spec)
             for k, v in new_stat.items():
                 stats[k].append(v)