diff --git a/indra/CMakeLists.txt b/indra/CMakeLists.txt
index 9f8c504409557601d11ea1a2736199a3103afb24..c8a793aaa5460bdb968a80153b0a0acaf9e38ce2 100644
--- a/indra/CMakeLists.txt
+++ b/indra/CMakeLists.txt
@@ -75,9 +75,10 @@ if (VIEWER)
     add_dependencies(viewer mac-updater mac-crash-logger)
   elseif (WINDOWS)
     add_subdirectory(${VIEWER_PREFIX}win_crash_logger)
-    if (EXISTS ${VIEWER_PREFIX}win_setup)
-      add_subdirectory(${VIEWER_PREFIX}win_setup)
-    endif (EXISTS ${VIEWER_PREFIX}win_setup)
+    # cmake EXISTS requires an absolute path, see indra/cmake/Variables.cmake
+    if (EXISTS ${VIEWER_DIR}win_setup)
+      add_subdirectory(${VIEWER_DIR}win_setup)
+    endif (EXISTS ${VIEWER_DIR}win_setup)
     add_subdirectory(${VIEWER_PREFIX}win_updater)
     # add_dependencies(viewer windows-updater windows-setup windows-crash-logger)
     add_dependencies(viewer windows-updater windows-crash-logger)