diff --git a/lib-src/emacsclient.c b/lib-src/emacsclient.c
index b28acb26da0..85d0bdebeb5 100644
--- a/lib-src/emacsclient.c
+++ b/lib-src/emacsclient.c
@@ -282,3 +282,18 @@ main (argc, argv)
 #endif /* HAVE_SYSVIPC */
 
 #endif /* HAVE_SOCKETS or HAVE_SYSVIPC */
+
+#ifndef HAVE_STRERROR
+char *
+strerror (errnum)
+     int errnum;
+{
+  extern char *sys_errlist[];
+  extern int sys_nerr;
+
+  if (errnum >= 0 && errnum < sys_nerr)
+    return sys_errlist[errnum];
+  return (char *) "Unknown error";
+}
+
+#endif /* ! HAVE_STRERROR */
diff --git a/lib-src/env.c b/lib-src/env.c
index 282a94069df..35532e0360d 100644
--- a/lib-src/env.c
+++ b/lib-src/env.c
@@ -333,3 +333,18 @@ myindex (str, c)
     }
   return 0;
 }
+
+#ifndef HAVE_STRERROR
+char *
+strerror (errnum)
+     int errnum;
+{
+  extern char *sys_errlist[];
+  extern int sys_nerr;
+
+  if (errnum >= 0 && errnum < sys_nerr)
+    return sys_errlist[errnum];
+  return (char *) "Unknown error";
+}
+
+#endif /* ! HAVE_STRERROR */
diff --git a/lib-src/timer.c b/lib-src/timer.c
index 8676b196597..cb7c4c0b2b1 100644
--- a/lib-src/timer.c
+++ b/lib-src/timer.c
@@ -300,5 +300,20 @@ main (argc, argv)
   for (;;)
     pause ();
 }
+
+#ifndef HAVE_STRERROR
+char *
+strerror (errnum)
+     int errnum;
+{
+  extern char *sys_errlist[];
+  extern int sys_nerr;
+
+  if (errnum >= 0 && errnum < sys_nerr)
+    return sys_errlist[errnum];
+  return (char *) "Unknown error";
+}
+
+#endif /* ! HAVE_STRERROR */
 
 /* timer.c ends here */