diff --git a/js/src/Makefile.in b/js/src/Makefile.in
index 5bba9ce489b..38b65f4bfed 100644
--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -257,8 +257,6 @@ endif
 
 EXPORTS = $(INSTALLED_HEADERS)
 
-JS_SAFE_ARENA	= 1
-
 DASH_R		= -r
 
 ifneq (,$(filter OS2 WINCE WINNT,$(OS_ARCH)))
@@ -365,10 +363,6 @@ ifneq (,$(CROSS_COMPILE)$(filter-out WINNT,$(OS_ARCH)))
 TARGETS		+= jscpucfg$(HOST_BIN_SUFFIX)
 endif
 
-ifdef JS_SAFE_ARENA
-DEFINES		+= -DJS_USE_SAFE_ARENA
-endif
-
 ifdef JS_THREADSAFE
 DEFINES		+= -DJS_THREADSAFE
 endif