diff --git a/indra/newview/app_settings/settings.xml b/indra/newview/app_settings/settings.xml
index 5a185a665d..acaeb40cf5 100644
--- a/indra/newview/app_settings/settings.xml
+++ b/indra/newview/app_settings/settings.xml
@@ -13742,7 +13742,7 @@
     <key>FullScreen</key>
     <map>
       <key>Comment</key>
-      <string>run a fullscreen session</string>
+      <string>Run a fullscreen session. MacOS not supported</string>
       <key>Persist</key>
       <integer>1</integer>
       <key>Type</key>
diff --git a/indra/newview/llappviewer.cpp b/indra/newview/llappviewer.cpp
index aea4492223..0581cbbee4 100644
--- a/indra/newview/llappviewer.cpp
+++ b/indra/newview/llappviewer.cpp
@@ -3088,7 +3088,15 @@ bool LLAppViewer::initWindow()
         .height(gSavedSettings.getU32("WindowHeight"))
         .min_width(gSavedSettings.getU32("MinWindowWidth"))
         .min_height(gSavedSettings.getU32("MinWindowHeight"))
+#ifdef LL_DARWIN
+        // Setting it to true causes black screen with no UI displayed.
+        // Given that it's a DEBUG settings and application goes fullscreen
+        // on mac simply by expanding it, it was decided to not support/use
+        // this setting on mac.
+        .fullscreen(false)
+#else // LL_DARWIN
         .fullscreen(gSavedSettings.getBOOL("FullScreen"))
+#endif
         .ignore_pixel_depth(ignorePixelDepth)
         .first_run(mIsFirstRun);