diff --git a/configure.ac b/configure.ac
index f131735460e..80991f3866c 100644
--- a/configure.ac
+++ b/configure.ac
@@ -3277,12 +3277,20 @@ if test "$emacs_cv_struct_alignment" = yes; then
      structure to an N-byte boundary.])
 fi
 
-# Check for alignas now rather than waiting for gl_INIT to do it,
-# as the system_malloc=no test below needs $gl_cv_header_working_stdalign_h.
-# Do not simply call gl_INIT here, as the ac_cv_func_pthread_sigmask=yes
-# assignment below affects how gl_INIT works.
-# Instead, call gl_ALIGNASOF, the only part of gl_INIT needed here.
-# Then make gl_ALIGNASOF a no-op so gl_INIT does not duplicate its code.
+dnl Work around a glitch if aclocal is invoked outside of autogen.sh.
+dnl Such an invocation generates an aclocal.m4 that lacks m4/stdalign.m4.
+dnl The following hack checks the otherwise-uninvolved macro gl_STDALIGN_H
+dnl so that the hack itself does not generate a diagnostic.
+m4_divert_push([KILL])
+m4_ifdef([gl_STDALIGN_H], [], [m4_include([m4/stdalign.m4])])
+m4_divert_pop([KILL])
+
+dnl Check for alignas now rather than waiting for gl_INIT to do it,
+dnl as the system_malloc=no test below needs $gl_cv_header_working_stdalign_h.
+dnl Do not simply call gl_INIT here, as the ac_cv_func_pthread_sigmask=yes
+dnl assignment below affects how gl_INIT works.
+dnl Instead, call gl_ALIGNASOF, the only part of gl_INIT needed here.
+dnl Then make gl_ALIGNASOF a no-op so gl_INIT does not duplicate its code.
 gl_ALIGNASOF
 AC_DEFUN([gl_ALIGNASOF])