diff --git a/test/README.vars b/test/README.vars
index 2157d9497db8..38029f7d4c45 100644
--- a/test/README.vars
+++ b/test/README.vars
@@ -1,3 +1,4 @@
 Environment variables in VCL:
 
 LO_TEST_LOCALE - the locale to be used during unit tests. Defaults to en-US.
+LIBO_TEST_DEFAULT_DESKTOP - define this to make tests run in current (active) desktop on Windows (by default, they run on a dedicated desktop, to avoid unwanted interaction with current UI session)
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diff --git a/uitest/README.md b/uitest/README.md
index 8c872bed6f27..e952d055c7b4 100644
--- a/uitest/README.md
+++ b/uitest/README.md
@@ -1,3 +1,7 @@
 # UI Testing Framework
 
 The code for the UI testing framework and the UI tests.
+
+The UI tests run on a dedicated desktop on Windows, to not interfere with the interactive session.
+To make them run on the current (active) desktop, define the following environment variable:
+LIBO_TEST_DEFAULT_DESKTOP
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