diff --git a/tests/Perspex.Base.UnitTests/Properties/AssemblyInfo.cs b/tests/Perspex.Base.UnitTests/Properties/AssemblyInfo.cs
index b011d2a1c4..1752a3b211 100644
--- a/tests/Perspex.Base.UnitTests/Properties/AssemblyInfo.cs
+++ b/tests/Perspex.Base.UnitTests/Properties/AssemblyInfo.cs
@@ -2,5 +2,9 @@
 // Licensed under the MIT license. See licence.md file in the project root for full license information.
 
 using System.Reflection;
+using Xunit;
 
 [assembly: AssemblyTitle("Perspex.UnitTests")]
+
+// Don't run tests in parallel.
+[assembly: CollectionBehavior(DisableTestParallelization = true)]
\ No newline at end of file