--- a/js/src/Makefile.in
+++ b/js/src/Makefile.in
@@ -632,18 +632,22 @@ endif
 
 ifdef GNU_CC
 imacro_asm.js: imacro_asm.js.in jsopcode.tbl
 	$(CC) -c -x c -E -P -I$(srcdir) $< > $@
 
 GARBAGE += imacros.c.out imacro_asm.js
 
 ifndef CROSS_COMPILE
+# Obsolete comment: if you replace update-imacros with libs, this would apply
+# but then parallel gmake would sometimes try to run $(DIST)/bin/js before it
+# had been built and installed. Want a fix for this, de-automating for now.
+
 # Build imacros.c.out after descending into DIRS and building the js shell.
 # This may result in an updated imacros.c.out file that requires a re-build
 # to stabilize.
-libs:: imacros.c.out
+update-imacros:: imacros.c.out
 	@cmp -s imacros.c.out $(srcdir)/$< || cp imacros.c.out $(srcdir)
 
 %.c.out: %.jsasm imacro_asm.js
 	$(DIST)/bin/js imacro_asm.js $< > $@
 endif
 endif