diff --git a/rebound/tests/test_mercurius.py b/rebound/tests/test_mercurius.py
index fdd81aee3..7799e21c2 100644
--- a/rebound/tests/test_mercurius.py
+++ b/rebound/tests/test_mercurius.py
@@ -2,6 +2,7 @@
 import unittest
 import sys
 import warnings
+import os
 from datetime import datetime
 
 class TestMercurius(unittest.TestCase):
@@ -312,7 +313,8 @@ def get_sim():
         # and are therefore machine dependent. 
         self.assertLess(dE_mercurius,5e-6)              # reasonable precision for mercurius
         self.assertLess(dE_mercurius/dE_whfast,1e-4)    # at least 1e4 times better than whfast
-        self.assertLess(time_mercurius,5.0*time_ias15)  # not much slower than ias15 (often fails in unit tests)
+        if os.getenv("CI") != "true":
+            self.assertLess(time_mercurius,5.0*time_ias15)  # not much slower than ias15 (often fails in unit tests)
         if sys.maxsize > 2**32: # 64 bit
             self.assertEqual(7060.644251181158, sim.particles[5].x) # Check if bitwise unchanged