diff --git a/src/expand-common.c b/src/expand-common.c
index 9c94441..41d7003 100644
--- a/src/expand-common.c
+++ b/src/expand-common.c
@@ -66,7 +66,7 @@ int exit_status = EXIT_SUCCESS;
 
 
 /* Add tab stop TABVAL to the end of 'tab_list'.  */
-void
+extern void
 add_tab_stop (uintmax_t tabval)
 {
   uintmax_t prev_column = first_free_tab ? tab_list[first_free_tab - 1] : 0;
@@ -86,7 +86,7 @@ add_tab_stop (uintmax_t tabval)
 
 /* Add the comma or blank separated list of tab stops STOPS
    to the list of tab stops.  */
-void
+extern void
 parse_tab_stops (char const *stops)
 {
   bool have_tabval = false;
@@ -165,7 +165,7 @@ validate_tab_stops (uintmax_t const *tabs, size_t entries)
    tab-stops = N (if value N specified as the only value).
    tab-stops = distinct values given on command line (if multiple values given).
 */
-void
+extern void
 finalize_tab_stops (void)
 {
   validate_tab_stops (tab_list, first_free_tab);
@@ -179,7 +179,7 @@ finalize_tab_stops (void)
 }
 
 
-uintmax_t
+extern uintmax_t
 get_next_tab_column (const uintmax_t column, size_t* tab_index,
                      bool* last_tab)
 {
@@ -206,7 +206,7 @@ get_next_tab_column (const uintmax_t column, size_t* tab_index,
 
 
 /* Sets new file-list */
-void
+extern void
 set_file_list (char **list)
 {
   have_read_stdin = false;
@@ -222,7 +222,7 @@ set_file_list (char **list)
    Open a filename of '-' as the standard input.
    Return NULL if there are no more input files.  */
 
-FILE *
+extern FILE *
 next_file (FILE *fp)
 {
   static char *prev_file;
@@ -266,7 +266,7 @@ next_file (FILE *fp)
 }
 
 /* */
-void
+extern void
 cleanup_file_list_stdin (void)
 {
     if (have_read_stdin && fclose (stdin) != 0)
diff --git a/src/expand-common.h b/src/expand-common.h
index 4d1074b..8cb2079 100644
--- a/src/expand-common.h
+++ b/src/expand-common.h
@@ -35,38 +35,38 @@ extern size_t max_column_width;
 extern int exit_status;
 
 /* Add tab stop TABVAL to the end of 'tab_list'.  */
-void
+extern void
 add_tab_stop (uintmax_t tabval);
 
 /* Add the comma or blank separated list of tab stops STOPS
    to the list of tab stops.  */
-void
+extern void
 parse_tab_stops (char const *stops);
 
 /* TODO: Document */
-uintmax_t
+extern uintmax_t
 get_next_tab_column (const uintmax_t column, size_t* tab_index,
                      bool* last_tab);
 
 /* Called after all command-line options have been parsed,
    sets the final tab-stops values */
-void
+extern void
 finalize_tab_stops (void);
 
 
 
 
 /* Sets new file-list */
-void
+extern void
 set_file_list (char **file_list);
 
 /* Close the old stream pointer FP if it is non-NULL,
    and return a new one opened to read the next input file.
    Open a filename of '-' as the standard input.
    Return NULL if there are no more input files.  */
-FILE *
+extern FILE *
 next_file (FILE *fp);
 
 /* */
-void
+extern void
 cleanup_file_list_stdin (void);