diff --git a/Src/Common/RootSite/RootSiteTests/RealDataTestsBase.cs b/Src/Common/RootSite/RootSiteTests/RealDataTestsBase.cs
index 8475864706..f5717a0f42 100644
--- a/Src/Common/RootSite/RootSiteTests/RealDataTestsBase.cs
+++ b/Src/Common/RootSite/RootSiteTests/RealDataTestsBase.cs
@@ -1,5 +1,7 @@
 using System;
 using System.IO;
+using System.Security.Cryptography;
+using System.Text;
 using System.Threading;
 using NUnit.Framework;
 using SIL.FieldWorks.Common.FwUtils;
@@ -20,11 +22,22 @@ namespace SIL.FieldWorks.Common.RootSites.RootSiteTests
 	[TestFixture]
 	public abstract class RealDataTestsBase
 	{
-		private const string ReusableProjectName = "integration_test_data";
-		private const string ProjectMutexName =
-			@"Local\FieldWorks.RealDataTests.integration_test_data";
+		// The project name must be unique per worktree, so that multiple worktrees of the same repo
+		// can run tests in parallel without colliding on the same project directory.
+		private static readonly string ReusableProjectName = "integration_test_data_" + WorktreeSuffix();
+		private static readonly string ProjectMutexName =
+			@"Local\FieldWorks.RealDataTests." + ReusableProjectName;
 		private const string TestProjectSentinelFileName = ".fieldworks-real-data-test-project";
 
+		private static string WorktreeSuffix()
+		{
+			using (var sha = SHA1.Create())
+			{
+				var hash = sha.ComputeHash(Encoding.UTF8.GetBytes(FwDirectoryFinder.SourceDirectory));
+				return BitConverter.ToString(hash, 0, 4).Replace("-", string.Empty).ToLowerInvariant();
+			}
+		}
+
 		protected FwNewLangProjectModel m_model;
 		protected LcmCache Cache;
 		protected string m_dbName;
@@ -138,6 +151,8 @@ public virtual void TestTearDown()
 
 		protected string DbDirectory(string name)
 		{
+			// CreateNewLangProj always creates here and can't be redirected; collision avoidance
+			// across worktrees comes from ReusableProjectName's worktree-hash suffix instead.
 			return Path.Combine(FwDirectoryFinder.ProjectsDirectory, name);
 		}