diff --git a/src/odoors/ODPrntf.c b/src/odoors/ODPrntf.c
index a1c6d67b4d45b183d6f009a1b4f2d19e683b5da3..c2ca57dda592600358b931d25c5f83ca2fcd74dc 100644
--- a/src/odoors/ODPrntf.c
+++ b/src/odoors/ODPrntf.c
@@ -68,7 +68,7 @@
  *
  *     Return: void
  */
-ODAPIDEF void ODVCALL od_printf(char *pszFormat,...)
+ODAPIDEF void ODVCALL od_printf(const char *pszFormat,...)
 {
    va_list pArgumentList;
    static char *pszWorkBuffer = NULL;
diff --git a/src/odoors/OpenDoor.h b/src/odoors/OpenDoor.h
index c206a5fc75e670ff42264804bb275a612ef0082c..c26e1b3f3d8a22877a7288cc6fa73ef6cfc677e7 100644
--- a/src/odoors/OpenDoor.h
+++ b/src/odoors/OpenDoor.h
@@ -996,7 +996,7 @@ ODAPIDEF void ODCALL   od_parse_cmd_line(INT nArgCount,
 #endif /* !ODPLAT_WIN32 */
 ODAPIDEF INT ODCALL    od_popup_menu(char *pszTitle, char *pszText,
                           INT nLeft, INT nTop, INT nLevel, WORD uFlags);
-ODAPIDEF void ODVCALL  od_printf(char *pszFormat, ...);
+ODAPIDEF void ODVCALL  od_printf(const char *pszFormat, ...);
 ODAPIDEF void ODCALL   od_putch(char chToDisplay);
 ODAPIDEF BOOL ODCALL   od_puttext(INT nLeft, INT nTop, INT nRight,
                           INT nBottom, void *pBlock);