diff --git a/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests/BuildScripts.cs b/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests/BuildScripts.cs
index 76ec2ccf1e9..ecb2e58174d 100644
--- a/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests/BuildScripts.cs
+++ b/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests/BuildScripts.cs
@@ -253,6 +253,7 @@ namespace Semmle.Autobuild.Cpp.Tests
             Actions.GetEnvironmentVariable[$"CODEQL_EXTRACTOR_{codeqlUpperLanguage}_TRAP_DIR"] = "";
             Actions.GetEnvironmentVariable[$"CODEQL_EXTRACTOR_{codeqlUpperLanguage}_SOURCE_ARCHIVE_DIR"] = "";
             Actions.GetEnvironmentVariable[$"CODEQL_EXTRACTOR_{codeqlUpperLanguage}_ROOT"] = $@"C:\codeql\{codeqlUpperLanguage.ToLowerInvariant()}";
+            Actions.GetEnvironmentVariable[$"CODEQL_EXTRACTOR_{codeqlUpperLanguage}_DIAGNOSTIC_DIR"] = Path.GetTempPath();
             Actions.GetEnvironmentVariable["CODEQL_JAVA_HOME"] = @"C:\codeql\tools\java";
             Actions.GetEnvironmentVariable["CODEQL_PLATFORM"] = "win64";
             Actions.GetEnvironmentVariable["SEMMLE_DIST"] = @"C:\odasa";