--- spack-src/tp/Texinfo/Convert/XSParagraph/xspara.c.org	2019-11-18 17:33:07.717005871 +0900
+++ spack-src/tp/Texinfo/Convert/XSParagraph/xspara.c	2019-11-18 17:34:56.318436594 +0900
@@ -248,6 +248,11 @@
 
   dTHX;
 
+#if PERL_VERSION > 27 || (PERL_VERSION == 27 && PERL_SUBVERSION > 8)
+  /* needed due to thread-safe locale handling in newer perls */
+  switch_to_global_locale();
+#endif
+
   if (setlocale (LC_CTYPE, "en_US.UTF-8")
       || setlocale (LC_CTYPE, "en_US.utf8"))
     goto success;
@@ -319,6 +324,10 @@
   else
     {
 success: ;
+#if PERL_VERSION > 27 || (PERL_VERSION == 27 && PERL_SUBVERSION > 8)
+      /* needed due to thread-safe locale handling in newer perls */
+      sync_locale();
+#endif
       free (utf8_locale);
       /*
       fprintf (stderr, "tried to set LC_CTYPE to UTF-8.\n");