diff --git a/source/tools/atlas/AtlasScript/ScriptInterface.h b/source/tools/atlas/AtlasScript/ScriptInterface.h
index ebc34d1ac4..c4cc3fc669 100644
--- a/source/tools/atlas/AtlasScript/ScriptInterface.h
+++ b/source/tools/atlas/AtlasScript/ScriptInterface.h
@@ -24,16 +24,14 @@
 # define XP_UNIX
 #endif // (we don't support XP_OS2 or XP_BEOS)
 
-// NOTE: This requires a threadsafe SpiderMonkey - make sure you compile it with
-// the right options, else it'll fail when linking (which might not be until runtime,
-// and then you'll wish you saw this comment before spending so much time investigating
-// the problem).
-// ((There are a few places where SM really needs to be told to be threadsafe, even
-// though we're not actually sharing runtimes between threads.))
-#define JS_THREADSAFE
-
 #include "js/jspubtd.h"
 
+#ifndef JS_THREADSAFE
+#error The editor requires a threadsafe version of SpiderMonkey. Something in the build system is broken if you see this error.
+#endif
+// (There are a few places where SM really needs to be told to be threadsafe, even
+// though we're not actually sharing runtimes between threads.)
+
 class wxWindow;
 class wxString;
 class wxPanel;
diff --git a/source/tools/atlas/wxJS/precompiled.h b/source/tools/atlas/wxJS/precompiled.h
index be9cd39ff5..86a8442c7c 100644
--- a/source/tools/atlas/wxJS/precompiled.h
+++ b/source/tools/atlas/wxJS/precompiled.h
@@ -9,8 +9,6 @@
 # define XP_UNIX
 #endif // (we don't support XP_OS2 or XP_BEOS)
 
-#define JS_THREADSAFE
-
 
 #ifdef _WIN32
 # pragma warning (disable: 4100) // "unreferenced formal parameter"