diff --git a/include/file_change_detection.h b/include/file_change_detection.h
index aaed0a9b6d..f5220745a9 100644
--- a/include/file_change_detection.h
+++ b/include/file_change_detection.h
@@ -16,9 +16,10 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <errno.h>
+#ifndef _FILE_CHANGE_DETECTION_H
+#define _FILE_CHANGE_DETECTION_H
+
 #include <stdbool.h>
-#include <stddef.h>
 #include <stdio.h>
 #include <sys/stat.h>
 #include <sys/types.h>
@@ -38,103 +39,32 @@ struct file_change_detection
 
 /* Returns true if *LEFT and *RIGHT describe the same version of the
    same file.  */
-static bool __attribute__ ((unused))
-file_is_unchanged (const struct file_change_detection *left,
-                   const struct file_change_detection *right)
-{
-  if (left->size < 0 || right->size < 0)
-    /* Negative sizes are used as markers and never match.  */
-    return false;
-  else if (left->size == 0 && right->size == 0)
-    /* Both files are empty or do not exist, so they have the same
-       content, no matter what the other fields indicate.  */
-    return true;
-  else
-    return left->size == right->size
-      && left->ino == right->ino
-      && left->mtime.tv_sec == right->mtime.tv_sec
-      && left->mtime.tv_nsec == right->mtime.tv_nsec
-      && left->ctime.tv_sec == right->ctime.tv_sec
-      && left->ctime.tv_nsec == right->ctime.tv_nsec;
-}
+bool __file_is_unchanged (const struct file_change_detection *left,
+                        const struct file_change_detection *right);
 
 /* Extract file change information to *FILE from the stat buffer
    *ST.  */
-static void __attribute__ ((unused))
-file_change_detection_for_stat (struct file_change_detection *file,
-                                const struct stat64 *st)
-{
-  if (S_ISDIR (st->st_mode))
-    /* Treat as empty file.  */
-    file->size = 0;
-  else if (!S_ISREG (st->st_mode))
-    /* Non-regular files cannot be cached.  */
-    file->size = -1;
-  else
-    {
-      file->size = st->st_size;
-      file->ino = st->st_ino;
-      file->mtime = st->st_mtim;
-      file->ctime = st->st_ctim;
-    }
-}
+void __file_change_detection_for_stat (struct file_change_detection *file,
+                                       const struct stat64 *st);
 
 /* Writes file change information for PATH to *FILE.  Returns true on
    success.  For benign errors, *FILE is cleared, and true is
    returned.  For errors indicating resource outages and the like,
    false is returned.  */
-static bool __attribute__ ((unused))
-file_change_detection_for_path (struct file_change_detection *file,
-                                const char *path)
-{
-  struct stat64 st;
-  if (stat64 (path, &st) != 0)
-    switch (errno)
-      {
-      case EACCES:
-      case EISDIR:
-      case ELOOP:
-      case ENOENT:
-      case ENOTDIR:
-      case EPERM:
-        /* Ignore errors due to file system contents.  Instead, treat
-           the file as empty.  */
-        file->size = 0;
-        return true;
-      default:
-        /* Other errors are fatal.  */
-        return false;
-      }
-  else /* stat64 was successfull.  */
-    {
-      file_change_detection_for_stat (file, &st);
-      return true;
-    }
-}
+bool __file_change_detection_for_path (struct file_change_detection *file,
+                                       const char *path);
 
 /* Writes file change information for the stream FP to *FILE.  Returns
    ture on success, false on failure.  If FP is NULL, treat the file
    as non-existing.  */
-static bool __attribute__ ((unused))
-file_change_detection_for_fp (struct file_change_detection *file,
-                              FILE *fp)
-{
-  if (fp == NULL)
-    {
-      /* The file does not exist.  */
-      file->size = 0;
-      return true;
-    }
-  else
-    {
-      struct stat64 st;
-      if (fstat64 (__fileno (fp), &st) != 0)
-        /* If we already have a file descriptor, all errors are fatal.  */
-        return false;
-      else
-        {
-          file_change_detection_for_stat (file, &st);
-          return true;
-        }
-    }
-}
+bool __file_change_detection_for_fp (struct file_change_detection *file,
+                                     FILE *fp);
+
+#ifndef _ISOMAC
+libc_hidden_proto (__file_is_unchanged)
+libc_hidden_proto (__file_change_detection_for_stat)
+libc_hidden_proto (__file_change_detection_for_path)
+libc_hidden_proto (__file_change_detection_for_fp)
+#endif
+
+#endif /* _FILE_CHANGE_DETECTION_H */
diff --git a/io/Makefile b/io/Makefile
index 04c4647dc0..cf380f3516 100644
--- a/io/Makefile
+++ b/io/Makefile
@@ -55,7 +55,7 @@ routines :=								\
 	posix_fadvise posix_fadvise64					\
 	posix_fallocate posix_fallocate64				\
 	sendfile sendfile64 copy_file_range 				\
-	utimensat futimens
+	utimensat futimens file_change_detection
 
 # These routines will be omitted from the libc shared object.
 # Instead the static object files will be included in a special archive
diff --git a/io/Versions b/io/Versions
index f7e5dbe49e..ee468055ff 100644
--- a/io/Versions
+++ b/io/Versions
@@ -137,5 +137,9 @@ libc {
     __fcntl_nocancel;
     __open64_nocancel;
     __write_nocancel;
+    __file_is_unchanged;
+    __file_change_detection_for_stat;
+    __file_change_detection_for_path;
+    __file_change_detection_for_fp;
   }
 }
diff --git a/io/file_change_detection.c b/io/file_change_detection.c
new file mode 100644
index 0000000000..1ac869c3ec
--- /dev/null
+++ b/io/file_change_detection.c
@@ -0,0 +1,129 @@
+/* Detecting file changes using modification times.
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <file_change_detection.h>
+
+#include <errno.h>
+#include <stddef.h>
+
+/* Returns true if *LEFT and *RIGHT describe the same version of the
+   same file.  */
+bool
+__file_is_unchanged (const struct file_change_detection *left,
+                     const struct file_change_detection *right)
+{
+  if (left->size < 0 || right->size < 0)
+    /* Negative sizes are used as markers and never match.  */
+    return false;
+  else if (left->size == 0 && right->size == 0)
+    /* Both files are empty or do not exist, so they have the same
+       content, no matter what the other fields indicate.  */
+    return true;
+  else
+    return left->size == right->size
+      && left->ino == right->ino
+      && left->mtime.tv_sec == right->mtime.tv_sec
+      && left->mtime.tv_nsec == right->mtime.tv_nsec
+      && left->ctime.tv_sec == right->ctime.tv_sec
+      && left->ctime.tv_nsec == right->ctime.tv_nsec;
+}
+libc_hidden_def (__file_is_unchanged)
+
+/* Extract file change information to *FILE from the stat buffer
+   *ST.  */
+void
+__file_change_detection_for_stat (struct file_change_detection *file,
+                                  const struct stat64 *st)
+{
+  if (S_ISDIR (st->st_mode))
+    /* Treat as empty file.  */
+    file->size = 0;
+  else if (!S_ISREG (st->st_mode))
+    /* Non-regular files cannot be cached.  */
+    file->size = -1;
+  else
+    {
+      file->size = st->st_size;
+      file->ino = st->st_ino;
+      file->mtime = st->st_mtim;
+      file->ctime = st->st_ctim;
+    }
+}
+libc_hidden_def (__file_change_detection_for_stat)
+
+/* Writes file change information for PATH to *FILE.  Returns true on
+   success.  For benign errors, *FILE is cleared, and true is
+   returned.  For errors indicating resource outages and the like,
+   false is returned.  */
+bool
+__file_change_detection_for_path (struct file_change_detection *file,
+                                  const char *path)
+{
+  struct stat64 st;
+  if (stat64 (path, &st) != 0)
+    switch (errno)
+      {
+      case EACCES:
+      case EISDIR:
+      case ELOOP:
+      case ENOENT:
+      case ENOTDIR:
+      case EPERM:
+        /* Ignore errors due to file system contents.  Instead, treat
+           the file as empty.  */
+        file->size = 0;
+        return true;
+      default:
+        /* Other errors are fatal.  */
+        return false;
+      }
+  else /* stat64 was successfull.  */
+    {
+      __file_change_detection_for_stat (file, &st);
+      return true;
+    }
+}
+libc_hidden_def (__file_change_detection_for_path)
+
+/* Writes file change information for the stream FP to *FILE.  Returns
+   ture on success, false on failure.  If FP is NULL, treat the file
+   as non-existing.  */
+bool
+__file_change_detection_for_fp (struct file_change_detection *file,
+                                FILE *fp)
+{
+  if (fp == NULL)
+    {
+      /* The file does not exist.  */
+      file->size = 0;
+      return true;
+    }
+  else
+    {
+      struct stat64 st;
+      if (fstat64 (__fileno (fp), &st) != 0)
+        /* If we already have a file descriptor, all errors are fatal.  */
+        return false;
+      else
+        {
+          __file_change_detection_for_stat (file, &st);
+          return true;
+        }
+    }
+}
+libc_hidden_def (__file_change_detection_for_fp)
diff --git a/io/tst-file_change_detection.c b/io/tst-file_change_detection.c
index 035dd39c4d..6e00e787b1 100644
--- a/io/tst-file_change_detection.c
+++ b/io/tst-file_change_detection.c
@@ -16,10 +16,6 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-/* The header uses the internal __fileno symbol, which is not
-   available outside of libc (even to internal tests).  */
-#define __fileno(fp) fileno (fp)
-
 #include <file_change_detection.h>
 
 #include <array_length.h>
@@ -40,7 +36,7 @@ all_same (struct file_change_detection *array, size_t length)
       {
         if (test_verbose > 0)
           printf ("info: comparing %zu and %zu\n", i, j);
-        TEST_VERIFY (file_is_unchanged (array + i, array + j));
+        TEST_VERIFY (__file_is_unchanged (array + i, array + j));
       }
 }
 
@@ -54,7 +50,7 @@ all_different (struct file_change_detection *array, size_t length)
           continue;
         if (test_verbose > 0)
           printf ("info: comparing %zu and %zu\n", i, j);
-        TEST_VERIFY (!file_is_unchanged (array + i, array + j));
+        TEST_VERIFY (!__file_is_unchanged (array + i, array + j));
       }
 }
 
@@ -105,24 +101,24 @@ do_test (void)
     struct file_change_detection fcd[10];
     int i = 0;
     /* Two empty files always have the same contents.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty1));
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty2));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_empty1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_empty2));
     /* So does a missing file (which is treated as empty).  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++],
-                                                 path_does_not_exist));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++],
+                                                   path_does_not_exist));
     /* And a symbolic link loop.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_loop));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_loop));
     /* And a dangling symbolic link.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_dangling));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_dangling));
     /* And a directory.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], tempdir));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], tempdir));
     /* And a symbolic link to an empty file.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_to_empty1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_to_empty1));
     /* Likewise for access the file via a FILE *.  */
-    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_empty1));
-    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_empty2));
+    TEST_VERIFY (__file_change_detection_for_fp (&fcd[i++], fp_empty1));
+    TEST_VERIFY (__file_change_detection_for_fp (&fcd[i++], fp_empty2));
     /* And a NULL FILE * (missing file).  */
-    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], NULL));
+    TEST_VERIFY (__file_change_detection_for_fp (&fcd[i++], NULL));
     TEST_COMPARE (i, array_length (fcd));
 
     all_same (fcd, array_length (fcd));
@@ -132,9 +128,9 @@ do_test (void)
   {
     struct file_change_detection fcd[3];
     int i = 0;
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file1));
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_to_file1));
-    TEST_VERIFY (file_change_detection_for_fp (&fcd[i++], fp_file1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_file1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_to_file1));
+    TEST_VERIFY (__file_change_detection_for_fp (&fcd[i++], fp_file1));
     TEST_COMPARE (i, array_length (fcd));
     all_same (fcd, array_length (fcd));
   }
@@ -144,20 +140,20 @@ do_test (void)
     struct file_change_detection fcd[5];
     int i = 0;
     /* The other files are not empty.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_empty1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_empty1));
     /* These two files have the same contents, but have different file
        identity.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file1));
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_file2));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_file1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_file2));
     /* FIFOs are always different, even with themselves.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_fifo));
-    TEST_VERIFY (file_change_detection_for_path (&fcd[i++], path_fifo));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_fifo));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[i++], path_fifo));
     TEST_COMPARE (i, array_length (fcd));
     all_different (fcd, array_length (fcd));
 
     /* Replacing the file with its symbolic link does not make a
        difference.  */
-    TEST_VERIFY (file_change_detection_for_path (&fcd[1], path_to_file1));
+    TEST_VERIFY (__file_change_detection_for_path (&fcd[1], path_to_file1));
     all_different (fcd, array_length (fcd));
   }
 
@@ -166,16 +162,17 @@ do_test (void)
   for (int use_stdio = 0; use_stdio < 2; ++use_stdio)
     {
       struct file_change_detection initial;
-      TEST_VERIFY (file_change_detection_for_path (&initial, path_file1));
+      TEST_VERIFY (__file_change_detection_for_path (&initial, path_file1));
       while (true)
         {
           support_write_file_string (path_file1, "line\n");
           struct file_change_detection current;
           if (use_stdio)
-            TEST_VERIFY (file_change_detection_for_fp (&current, fp_file1));
+            TEST_VERIFY (__file_change_detection_for_fp (&current, fp_file1));
           else
-            TEST_VERIFY (file_change_detection_for_path (&current, path_file1));
-          if (!file_is_unchanged (&initial, &current))
+            TEST_VERIFY (__file_change_detection_for_path
+                         (&current, path_file1));
+          if (!__file_is_unchanged (&initial, &current))
             break;
           /* Wait for a bit to reduce system load.  */
           usleep (100 * 1000);
diff --git a/resolv/res_init.c b/resolv/res_init.c
index 98d84f264d..ee5dfdd391 100644
--- a/resolv/res_init.c
+++ b/resolv/res_init.c
@@ -583,7 +583,7 @@ __resolv_conf_load (struct __res_state *preinit,
   if (ok && change != NULL)
     /* Update the file change information if the configuration was
        loaded successfully.  */
-    ok = file_change_detection_for_fp (change, fp);
+    ok = __file_change_detection_for_fp (change, fp);
 
   if (ok)
     {
diff --git a/resolv/resolv_conf.c b/resolv/resolv_conf.c
index 29a1f4fb94..286149ffad 100644
--- a/resolv/resolv_conf.c
+++ b/resolv/resolv_conf.c
@@ -121,7 +121,7 @@ struct resolv_conf *
 __resolv_conf_get_current (void)
 {
   struct file_change_detection initial;
-  if (!file_change_detection_for_path (&initial, _PATH_RESCONF))
+  if (!__file_change_detection_for_path (&initial, _PATH_RESCONF))
     return NULL;
 
   struct resolv_conf_global *global_copy = get_locked_global ();
@@ -129,7 +129,7 @@ __resolv_conf_get_current (void)
     return NULL;
   struct resolv_conf *conf;
   if (global_copy->conf_current != NULL
-      && file_is_unchanged (&initial, &global_copy->file_resolve_conf))
+      && __file_is_unchanged (&initial, &global_copy->file_resolve_conf))
     /* We can reuse the cached configuration object.  */
     conf = global_copy->conf_current;
   else
@@ -149,7 +149,7 @@ __resolv_conf_get_current (void)
              /etc/resolv.conf is temporarily replaced while the file
              is read (after the initial measurement), and restored to
              the initial version later.  */
-          if (file_is_unchanged (&initial, &after_load))
+          if (__file_is_unchanged (&initial, &after_load))
             global_copy->file_resolve_conf = after_load;
           else
             /* If there is a discrepancy, trigger a reload during the
