diff --git a/tests/pkg_c25519/tests/01-run.py b/tests/pkg_c25519/tests/01-run.py
index f049f3179c..51f1df742f 100755
--- a/tests/pkg_c25519/tests/01-run.py
+++ b/tests/pkg_c25519/tests/01-run.py
@@ -14,7 +14,8 @@ import sys
 def testfunc(child):
     board = os.environ['BOARD']
     # Increase timeout on "real" hardware
-    timeout = 20 if board is not 'native' else -1
+    # 170 seconds on `arduino-mega2560`
+    timeout = 200 if board is not 'native' else -1
     child.expect(r"OK \(2 tests\)", timeout=timeout)