diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 40487a1..d593a1d 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -15,18 +15,18 @@ strategy:
     #Python37_windows:
     #  python.version: '3.7'
     #  vmImage: 'vs2017-win2016'
-    py36_linux:
-      python.version: '3.6'
-      vmImage: 'ubuntu-latest'
     py37_linux:
       python.version: '3.7'
       vmImage: 'ubuntu-latest'
-    py36_macOS:
-      vmImage: 'xcode9-macOS10.13'
-      python.version: '3.6'
+    py38_linux:
+      python.version: '3.8'
+      vmImage: 'ubuntu-latest'
     py37_macOS:
-      vmImage: 'xcode9-macOS10.13'
+      vmImage: 'macOS-latest'
       python.version: '3.7'
+    py38_macOS:
+      vmImage: 'macOS-latest'
+      python.version: '3.8'
 
 pool:
   vmImage: '$(vmImage)'
diff --git a/streamtracer/streamline.py b/streamtracer/streamline.py
index 83383fe..af75cb8 100755
--- a/streamtracer/streamline.py
+++ b/streamtracer/streamline.py
@@ -220,11 +220,11 @@ def trace(self, seeds, grid, direction=0):
                 seeds, field, grid_spacing, -1, self.max_steps, cyclic)
 
             # Reduce the size of the arrays, and flip the reverse streamlines
-            xs_f = np.array([xi[:ni, :] for xi, ni in zip(xs_f, ns_f)])
-            xs_r = np.array([xi[ni - 1:0:-1, :] for xi, ni in zip(xs_r, ns_r)])
+            xs_f = [xi[:ni, :] for xi, ni in zip(xs_f, ns_f)]
+            xs_r = [xi[ni - 1:0:-1, :] for xi, ni in zip(xs_r, ns_r)]
 
             # Stack the forward and reverse arrays
-            self.xs = np.array([np.vstack([xri, xfi]) for xri, xfi in zip(xs_r, xs_f)])
+            self.xs = [np.vstack([xri, xfi]) for xri, xfi in zip(xs_r, xs_f)]
             self.n_lines = np.fromiter([len(xsi) for xsi in self.xs], int)
 
             self.ROT = np.vstack([ROT_f, ROT_r]).T