diff --git a/include/ircd/js/js.h b/include/ircd/js/js.h
index 0c1dbbfd0..8fc678e10 100644
--- a/include/ircd/js/js.h
+++ b/include/ircd/js/js.h
@@ -33,6 +33,14 @@
 #pragma once
 #define HAVE_IRCD_JS_JS_H
 
+// SpiderMonkey makes use of the `DEBUG` define in headers which must match what the bottom
+// end was also compiled with. We tie that define to RB_DEBUG controlled by --enable-debug.
+// From a completely clean build, configuring IRCd with --enable-debug should compile SpiderMonkey
+// in debug as well.
+#ifdef RB_DEBUG
+	#define DEBUG
+#endif
+
 // SpiderMonkey headers require an include basis e.g. -I/usr/include/mozjs-XX as their
 // include directives are written as "jsxxx.h" or "mozilla/xxx.h" etc. Our includes are all
 // <ircd/xxx.h> and shouldn't have any conflict issues.
diff --git a/ircd/js.cc b/ircd/js.cc
index fa41067b8..9f9f39d4c 100644
--- a/ircd/js.cc
+++ b/ircd/js.cc
@@ -137,6 +137,9 @@ js::ReportOutOfMemory(ExclusiveContext *const c)
 	std::terminate();
 }
 
+// This was only ever defined for the SpiderMonkey headers and some of our hacks above.
+#undef DEBUG
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // ircd/js/js.h - With 3rd party (JSAPI) symbols