diff --git a/cat/virt-filesystems.c b/cat/virt-filesystems.c
index 46f813c29..4eb00e936 100644
--- a/cat/virt-filesystems.c
+++ b/cat/virt-filesystems.c
@@ -841,35 +841,6 @@ parents_of_vg (char *vg)
   return ret;
 }
 
-static char *
-join_comma (char **strings)
-{
-  size_t i, count;
-  char *ret;
-
-  for (count = i = 0; strings[i] != NULL; ++i) {
-    if (i > 0)
-      count++;
-    count += strlen (strings[i]);
-  }
-
-  ret = malloc (count + 1);
-  if (ret == NULL) {
-    perror ("malloc");
-    exit (EXIT_FAILURE);
-  }
-
-  for (count = i = 0; strings[i] != NULL; ++i) {
-    if (i > 0)
-      ret[count++] = ',';
-    strcpy (&ret[count], strings[i]);
-    count += strlen (strings[i]);
-  }
-  ret[count] = 0;
-
-  return ret;
-}
-
 static void
 write_row (const char *name, const char *type,
            const char *vfs_type, const char *vfs_label, int mbr_id,
@@ -916,7 +887,7 @@ write_row (const char *name, const char *type,
   }
   if ((columns & COLUMN_PARENTS)) {
     /* Internally comma-separated field. */
-    parents_str = join_comma (parents);
+    parents_str = guestfs___join_strings (",", parents);
     strings[len++] = parents_str;
   }
   if ((columns & COLUMN_UUID))
diff --git a/src/guestfs-internal-frontend.h b/src/guestfs-internal-frontend.h
index eba1c0e01..c8d8da02c 100644
--- a/src/guestfs-internal-frontend.h
+++ b/src/guestfs-internal-frontend.h
@@ -94,6 +94,8 @@ extern char *guestfs___safe_asprintf (guestfs_h *g, const char *fs, ...)
 /* utils.c */
 extern void guestfs___free_string_list (char **);
 extern size_t guestfs___count_strings (char *const *);
+extern char *guestfs___concat_strings (char *const *);
+extern char *guestfs___join_strings (const char *sep, char *const *);
 extern char *guestfs___exit_status_to_string (int status, const char *cmd_name, char *buffer, size_t buflen);
 extern int guestfs___random_string (char *ret, size_t len);
 extern char *guestfs___drive_name (size_t index, char *ret);
diff --git a/src/utils.c b/src/utils.c
index 54d9d7eeb..f8d2509d3 100644
--- a/src/utils.c
+++ b/src/utils.c
@@ -60,6 +60,48 @@ guestfs___count_strings (char *const *argv)
   return r;
 }
 
+/* Note that near-identical functions exist in the daemon. */
+char *
+guestfs___concat_strings (char *const *argv)
+{
+  return guestfs___join_strings ("", argv);
+}
+
+char *
+guestfs___join_strings (const char *sep, char *const *argv)
+{
+  size_t i, len, seplen, rlen;
+  char *r;
+
+  seplen = strlen (sep);
+
+  len = 0;
+  for (i = 0; argv[i] != NULL; ++i) {
+    if (i > 0)
+      len += seplen;
+    len += strlen (argv[i]);
+  }
+  len++; /* for final \0 */
+
+  r = malloc (len);
+  if (r == NULL)
+    return NULL;
+
+  rlen = 0;
+  for (i = 0; argv[i] != NULL; ++i) {
+    if (i > 0) {
+      memcpy (&r[rlen], sep, seplen);
+      rlen += seplen;
+    }
+    len = strlen (argv[i]);
+    memcpy (&r[rlen], argv[i], len);
+    rlen += len;
+  }
+  r[rlen] = '\0';
+
+  return r;
+}
+
 /* Translate a wait/system exit status into a printable string.  The
  * string must be freed by the caller.
  */