diff --git a/js/src/configure.in b/js/src/configure.in
index 6fede115305a..79df243fe343 100644
--- a/js/src/configure.in
+++ b/js/src/configure.in
@@ -1564,6 +1564,7 @@ case "$target" in
     ;;
 
 *-darwin*)
+    AC_DEFINE(XP_DARWIN)
     MKSHLIB='$(CXX) $(CXXFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MKCSHLIB='$(CC) $(CFLAGS) $(DSO_PIC_CFLAGS) $(DSO_LDOPTS) -o $@'
     MOZ_OPTIMIZE_FLAGS="-O3 -fno-stack-protector"