diff --git a/ChangeLog b/ChangeLog
index cf663d1b5f..4b8371a148 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,12 @@
 2017-04-07  Zack Weinberg  <zackw@panix.com>
 
+	* posix/getopt.c: When used standalone, define __libc_use_alloca
+	as always false and alloca to abort if called.
+	(process_long_option): Rewrite handling of ambiguous long options
+	to use a single boolean vector, not a linked list; use
+	__libc_use_alloca to decide whether to allocate this using alloca.
+	* posix/tst-getopt_long1.c: Adjust text of expected error message.
+
 	* posix/getopt.c (process_long_option): New function split out
 	from _getopt_internal_r.
 	(_getopt_internal_r): Replace both copies of the long-option
diff --git a/posix/getopt.c b/posix/getopt.c
index ecb9923a6e..79c81ae2f1 100644
--- a/posix/getopt.c
+++ b/posix/getopt.c
@@ -51,6 +51,10 @@
 #  define flockfile(fp) /* nop */
 #  define funlockfile(fp) /* nop */
 # endif
+/* When used standalone, do not attempt to use alloca.  */
+# define __libc_use_alloca(size) 0
+# undef alloca
+# define alloca(size) (abort (), (void *)0)
 #endif
 
 /* This implementation of 'getopt' has three modes for handling
@@ -197,150 +201,179 @@ process_long_option (int argc, char **argv, const char *optstring,
   size_t namelen;
   const struct option *p;
   const struct option *pfound = NULL;
-  struct option_list
-  {
-    const struct option *p;
-    struct option_list *next;
-  } *ambig_list = NULL;
-  int exact = 0;
-  int indfound = -1;
+  int n_options;
   int option_index;
 
   for (nameend = d->__nextchar; *nameend && *nameend != '='; nameend++)
     /* Do nothing.  */ ;
   namelen = nameend - d->__nextchar;
 
-  /* Test all long options for either exact match
-     or abbreviated matches.  */
-  for (p = longopts, option_index = 0; p->name; p++, option_index++)
-    if (!strncmp (p->name, d->__nextchar, namelen))
+  /* First look for an exact match, counting the options as a side
+     effect.  */
+  for (p = longopts, n_options = 0; p->name; p++, n_options++)
+    if (!strncmp (p->name, d->__nextchar, namelen)
+	&& namelen == strlen (p->name))
       {
-        if (namelen == strlen (p->name))
-          {
-            /* Exact match found.  */
-            pfound = p;
-            indfound = option_index;
-            exact = 1;
-            break;
-          }
-        else if (pfound == NULL)
-          {
-            /* First nonexact match found.  */
-            pfound = p;
-            indfound = option_index;
-          }
-        else if (long_only
-                 || pfound->has_arg != p->has_arg
-                 || pfound->flag != p->flag
-                 || pfound->val != p->val)
-          {
-            /* Second or later nonexact match found.  */
-            struct option_list *newp = alloca (sizeof (*newp));
-            newp->p = p;
-            newp->next = ambig_list;
-            ambig_list = newp;
-          }
+	/* Exact match found.  */
+	pfound = p;
+	option_index = n_options;
+	break;
       }
 
-  if (ambig_list != NULL && !exact)
+  if (pfound == NULL)
     {
-      if (print_errors)
-        {
-          struct option_list first;
-          first.p = pfound;
-          first.next = ambig_list;
-          ambig_list = &first;
+      /* Didn't find an exact match, so look for abbreviations.  */
+      unsigned char *ambig_set = NULL;
+      int ambig_malloced = 0;
+      int ambig_fallback = 0;
+      int indfound = -1;
 
-          flockfile (stderr);
+      for (p = longopts, option_index = 0; p->name; p++, option_index++)
+	if (!strncmp (p->name, d->__nextchar, namelen))
+	  {
+	    if (pfound == NULL)
+	      {
+		/* First nonexact match found.  */
+		pfound = p;
+		indfound = option_index;
+	      }
+	    else if (long_only
+		     || pfound->has_arg != p->has_arg
+		     || pfound->flag != p->flag
+		     || pfound->val != p->val)
+	      {
+		/* Second or later nonexact match found.  */
+		if (!ambig_fallback)
+		  {
+		    if (!print_errors)
+		      /* Don't waste effort tracking the ambig set if
+			 we're not going to print it anyway.  */
+		      ambig_fallback = 1;
+		    else if (!ambig_set)
+		      {
+			if (__libc_use_alloca (n_options))
+			  ambig_set = alloca (n_options);
+			else if ((ambig_set = malloc (n_options)) == NULL)
+			  /* Fall back to simpler error message.  */
+			  ambig_fallback = 1;
+			else
+			  ambig_malloced = 1;
 
-          fprintf (stderr, _("%s: option '%s' is ambiguous; possibilities:"),
-                   argv[0], argv[d->optind]);
-          do
-            {
-              fprintf (stderr, " '--%s'", ambig_list->p->name);
-              ambig_list = ambig_list->next;
-            }
-          while (ambig_list != NULL);
+			if (ambig_set)
+			  {
+			    memset (ambig_set, 0, n_options);
+			    ambig_set[indfound] = 1;
+			  }
+		      }
+		    if (ambig_set)
+		      ambig_set[option_index] = 1;
+		  }
+	      }
+	  }
 
-          /* This must use 'fprintf' even though it's only printing a
-             single character, so that it goes through __fxprintf_nocancel
-             when compiled as part of glibc.  */
-          fprintf (stderr, "\n");
-          funlockfile (stderr);
-        }
-      d->__nextchar += strlen (d->__nextchar);
-      d->optind++;
-      d->optopt = 0;
-      return '?';
-    }
+      if (ambig_set || ambig_fallback)
+	{
+	  if (print_errors)
+	    {
+	      if (ambig_fallback)
+		fprintf (stderr, _("%s: option '%s%s' is ambiguous\n"),
+			 argv[0], prefix, d->__nextchar);
+	      else
+		{
+		  flockfile (stderr);
+		  fprintf (stderr,
+			   _("%s: option '%s%s' is ambiguous; possibilities:"),
+			   argv[0], prefix, d->__nextchar);
+
+		  for (option_index = 0; option_index < n_options; option_index++)
+		    if (ambig_set[option_index])
+		      fprintf (stderr, " '%s%s'",
+			       prefix, longopts[option_index].name);
+
+		  /* This must use 'fprintf' even though it's only
+		     printing a single character, so that it goes through
+		     __fxprintf_nocancel when compiled as part of glibc.  */
+		  fprintf (stderr, "\n");
+		  funlockfile (stderr);
+		}
+	    }
+	  if (ambig_malloced)
+	    free (ambig_set);
+	  d->__nextchar += strlen (d->__nextchar);
+	  d->optind++;
+	  d->optopt = 0;
+	  return '?';
+	}
 
-  if (pfound != NULL)
-    {
       option_index = indfound;
-      d->optind++;
-      if (*nameend)
-        {
-          /* Don't test has_arg with >, because some C compilers don't
-             allow it to be used on enums.  */
-          if (pfound->has_arg)
-            d->optarg = nameend + 1;
-          else
-            {
-              if (print_errors)
-                fprintf (stderr,
-                         _("%s: option '%s%s' doesn't allow an argument\n"),
-                         argv[0], prefix, pfound->name);
-
-              d->__nextchar += strlen (d->__nextchar);
-              d->optopt = pfound->val;
-              return '?';
-            }
-        }
-      else if (pfound->has_arg == 1)
-        {
-          if (d->optind < argc)
-            d->optarg = argv[d->optind++];
-          else
-            {
-              if (print_errors)
-                fprintf (stderr,
-                         _("%s: option '%s%s' requires an argument\n"),
-                         argv[0], prefix, pfound->name);
-
-              d->__nextchar += strlen (d->__nextchar);
-              d->optopt = pfound->val;
-              return optstring[0] == ':' ? ':' : '?';
-            }
-        }
-      d->__nextchar += strlen (d->__nextchar);
-      if (longind != NULL)
-        *longind = option_index;
-      if (pfound->flag)
-        {
-          *(pfound->flag) = pfound->val;
-          return 0;
-        }
-      return pfound->val;
     }
 
-  /* Can't find it as a long option.  If this is not getopt_long_only,
-     or the option starts with '--' or is not a valid short option,
-     then it's an error.  */
-  if (!long_only || argv[d->optind][1] == '-'
-      || strchr (optstring, *d->__nextchar) == NULL)
+  if (pfound == NULL)
     {
-      if (print_errors)
-        fprintf (stderr, _("%s: unrecognized option '%s%s'\n"),
-                 argv[0], prefix, d->__nextchar);
+      /* Can't find it as a long option.  If this is not getopt_long_only,
+	 or the option starts with '--' or is not a valid short option,
+	 then it's an error.  */
+      if (!long_only || argv[d->optind][1] == '-'
+	  || strchr (optstring, *d->__nextchar) == NULL)
+	{
+	  if (print_errors)
+	    fprintf (stderr, _("%s: unrecognized option '%s%s'\n"),
+		     argv[0], prefix, d->__nextchar);
 
-      d->__nextchar = NULL;
-      d->optind++;
-      d->optopt = 0;
-      return '?';
+	  d->__nextchar = NULL;
+	  d->optind++;
+	  d->optopt = 0;
+	  return '?';
+	}
+
+      /* Otherwise interpret it as a short option.  */
+      return -1;
     }
 
-  /* Otherwise interpret it as a short option.  */
-  return -1;
+  /* We have found a matching long option.  Consume it.  */
+  d->optind++;
+  d->__nextchar = NULL;
+  if (*nameend)
+    {
+      /* Don't test has_arg with >, because some C compilers don't
+	 allow it to be used on enums.  */
+      if (pfound->has_arg)
+	d->optarg = nameend + 1;
+      else
+	{
+	  if (print_errors)
+	    fprintf (stderr,
+		     _("%s: option '%s%s' doesn't allow an argument\n"),
+		     argv[0], prefix, pfound->name);
+
+	  d->optopt = pfound->val;
+	  return '?';
+	}
+    }
+  else if (pfound->has_arg == 1)
+    {
+      if (d->optind < argc)
+	d->optarg = argv[d->optind++];
+      else
+	{
+	  if (print_errors)
+	    fprintf (stderr,
+		     _("%s: option '%s%s' requires an argument\n"),
+		     argv[0], prefix, pfound->name);
+
+	  d->optopt = pfound->val;
+	  return optstring[0] == ':' ? ':' : '?';
+	}
+    }
+
+  if (longind != NULL)
+    *longind = option_index;
+  if (pfound->flag)
+    {
+      *(pfound->flag) = pfound->val;
+      return 0;
+    }
+  return pfound->val;
 }
 
 /* Initialize internal data upon the first call to getopt.  */
diff --git a/posix/tst-getopt_long1.c b/posix/tst-getopt_long1.c
index 3895ebd99b..6d8ef02ca4 100644
--- a/posix/tst-getopt_long1.c
+++ b/posix/tst-getopt_long1.c
@@ -56,7 +56,7 @@ do_test (void)
   printf ("message = \"%s\"\n", line);
 
   static const char expected[] = "\
-program: option '--on' is ambiguous; possibilities: '--one' '--onto' '--one-one'\n";
+program: option '--on' is ambiguous; possibilities: '--one' '--one-one' '--onto'\n";
 
   return c != '?' || strcmp (line, expected) != 0;
 }