diff --git a/doc/install_windows_manually.txt b/doc/install_windows_manually.txt
index 50776e6efa..7437b4d3dd 100644
--- a/doc/install_windows_manually.txt
+++ b/doc/install_windows_manually.txt
@@ -64,6 +64,9 @@ parameter:
 
   install_super.bat secondservice
 
+NOTE: If you are running multiple Firebird services it is essential that you 
+do not configure the FIREBIRD environment variable at the system level.
+
 
 Uninstallation
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