diff --git a/src/editfns.c b/src/editfns.c
index cb7353a48c6..7e35fe87972 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -48,6 +48,16 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <float.h>
 #include <limits.h>
 
+#ifdef HAVE_TIMEZONE_T
+# include <sys/param.h>
+# if defined __NetBSD_Version__ && __NetBSD_Version__ < 700000000
+#  define HAVE_TZALLOC_BUG true
+# endif
+#endif
+#ifndef HAVE_TZALLOC_BUG
+# define HAVE_TZALLOC_BUG false
+#endif
+
 #include <c-ctype.h>
 #include <intprops.h>
 #include <stdlib.h>
@@ -205,16 +215,14 @@ tzlookup (Lisp_Object zone, bool settz)
 
       new_tz = tzalloc (zone_string);
 
-#if defined __NetBSD_Version__ && __NetBSD_Version__ < 700000000
-      /* NetBSD 6 tzalloc mishandles POSIX TZ strings (Bug#30738).
-	 If possible, fall back on tzdb.  */
-      if (!new_tz && errno != ENOMEM && plain_integer
+      if (HAVE_TZALLOC_BUG && !new_tz && errno != ENOMEM && plain_integer
 	  && XINT (zone) % (60 * 60) == 0)
 	{
+	  /* tzalloc mishandles POSIX strings; fall back on tzdb if
+	     possible (Bug#30738).  */
 	  sprintf (tzbuf, "Etc/GMT%+"pI"d", - (XINT (zone) / (60 * 60)));
 	  new_tz = tzalloc (zone_string);
 	}
-#endif
 
       if (!new_tz)
 	{