diff --git a/usr.bin/sort/file.c b/usr.bin/sort/file.c
index 59752012eda2..58a97826916e 100644
--- a/usr.bin/sort/file.c
+++ b/usr.bin/sort/file.c
@@ -227,7 +227,7 @@ file_list_init(struct file_list *fl, bool tmp)
  * Add a file name to the list
  */
 void
-file_list_add(struct file_list *fl, char *fn, bool allocate)
+file_list_add(struct file_list *fl, const char *fn, bool allocate)
 {
 
 	if (fl && fn) {
@@ -1115,7 +1115,7 @@ file_headers_merge(size_t fnum, struct file_header **fh, FILE *f_out)
  * stdout.
  */
 static void
-merge_files_array(size_t argc, char **argv, const char *fn_out)
+merge_files_array(size_t argc, const char **argv, const char *fn_out)
 {
 
 	if (argv && fn_out) {
diff --git a/usr.bin/sort/file.h b/usr.bin/sort/file.h
index f3a7d3abc022..724928a7c050 100644
--- a/usr.bin/sort/file.h
+++ b/usr.bin/sort/file.h
@@ -66,7 +66,7 @@ struct file_reader;
  */
 struct file_list
 {
-	char			**fns;
+	const char *		*fns;
 	size_t			 count;
 	size_t			 sz;
 	bool			 tmp;
@@ -108,7 +108,7 @@ char *new_tmp_file_name(void);
 void tmp_file_atexit(const char *tmp_file);
 
 void file_list_init(struct file_list *fl, bool tmp);
-void file_list_add(struct file_list *fl, char *fn, bool allocate);
+void file_list_add(struct file_list *fl, const char *fn, bool allocate);
 void file_list_populate(struct file_list *fl, int argc, char **argv, bool allocate);
 void file_list_clean(struct file_list *fl);
 
diff --git a/usr.bin/sort/sort.c b/usr.bin/sort/sort.c
index 5edc5af6703e..bbe8af4607bd 100644
--- a/usr.bin/sort/sort.c
+++ b/usr.bin/sort/sort.c
@@ -1299,7 +1299,11 @@ main(int argc, char **argv)
 		struct file_list fl;
 
 		file_list_init(&fl, false);
-		file_list_populate(&fl, argc, argv, true);
+		/* No file arguments remaining means "read from stdin." */
+		if (argc == 0)
+			file_list_add(&fl, "-", true);
+		else
+			file_list_populate(&fl, argc, argv, true);
 		merge_files(&fl, outfile);
 		file_list_clean(&fl);
 	}