diff --git a/src/Makefile.in b/src/Makefile.in
index 0326b4a8f22..6d75e3537a6 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -803,6 +803,15 @@ elnlisp := $(addprefix ${lispsource}/,${elnlisp}) $(lisp:.elc=.eln)
 	@$(MAKE) $(AM_V_NO_PD) -C ../lisp EMACS="../src/emacs$(EXEEXT)"\
 		THEFILE=$< $<n
 
+## FIXME: this is fragile!  We lie to Make about the files produced by
+## this rule, and we rely on the absence of the native-lisp directory
+## to trigger it.  This means that if anything goes wrong during
+## native compilation, the only way to trigger it again is to remove
+## the directory and re-native-compile everything.  The main
+## underlying problem is that the name of the subdirectory of
+## native-lisp where the *.eln files will be produced, and the exact
+## names of those *.eln files, cannot be known in advance; we must ask
+## Emacs to produce them.
 ../native-lisp: | $(pdmp)
 	@if test ! -d $@; then \
 	  mkdir $@ && $(MAKE) $(AM_V_NO_PD) $(elnlisp); \