diff --git a/tests/test_fits.py b/tests/test_fits.py
index e34e1d14..470c6a74 100644
--- a/tests/test_fits.py
+++ b/tests/test_fits.py
@@ -9,6 +9,8 @@ from scipy.odr import ODR, Model, Data, RealData
 import pyerrors as pe
 import pytest
 
+np.random.seed(0)
+
 def test_standard_fit():
     dim = 10 + int(30 * np.random.rand())
     x = np.arange(dim)
diff --git a/tests/test_linalg.py b/tests/test_linalg.py
index 9d7f6377..e13c80d5 100644
--- a/tests/test_linalg.py
+++ b/tests/test_linalg.py
@@ -11,6 +11,8 @@ from scipy.odr import ODR, Model, Data, RealData
 import pyerrors as pe
 import pytest
 
+np.random.seed(0)
+
 def test_matrix_functions():
     dim = 3 + int(4 * np.random.rand())
     print(dim)
diff --git a/tests/test_pyerrors.py b/tests/test_pyerrors.py
index 393cde8d..fcc00e6d 100644
--- a/tests/test_pyerrors.py
+++ b/tests/test_pyerrors.py
@@ -6,6 +6,8 @@ import copy
 import pyerrors as pe
 import pytest
 
+np.random.seed(0)
+
 def test_dump():
     value = np.random.normal(5, 10)
     dvalue = np.abs(np.random.normal(0, 1))
diff --git a/tests/test_roots.py b/tests/test_roots.py
index a6ce3d65..dce0eb45 100644
--- a/tests/test_roots.py
+++ b/tests/test_roots.py
@@ -2,7 +2,9 @@ import numpy as np
 import pyerrors as pe
 import pytest
 
-def test_find_root():
+np.random.seed(0)
+
+def test_root_linear():
 
     def root_function(x, d):
         return x - d
@@ -12,3 +14,6 @@ def test_find_root():
     my_root = pe.roots.find_root(my_obs, root_function)
 
     assert np.isclose(my_root.value, value)
+    difference = my_obs - my_root
+    assert all(np.isclose(0.0, difference.deltas['t']))
+