diff --git a/include/asterisk/features.h b/include/asterisk/features.h
index 1a5d760f388af15ba69c9dce1c4caa1fdd85b6d4..5e9d5f3d2de669a583492c4ad28f8f7a41c70930 100644
--- a/include/asterisk/features.h
+++ b/include/asterisk/features.h
@@ -73,10 +73,10 @@ int ast_masq_park_call(struct ast_channel *rchan, struct ast_channel *host, int
 /*! \brief Determine system parking extension
  *  Returns the call parking extension for drivers that provide special
     call parking help */
-char *ast_parking_ext(void);
+const char *ast_parking_ext(void);
 
 /*! \brief Determine system call pickup extension */
-char *ast_pickup_ext(void);
+const char *ast_pickup_ext(void);
 
 /*! \brief Bridge a call, optionally allowing redirection */
 int ast_bridge_call(struct ast_channel *chan, struct ast_channel *peer,struct ast_bridge_config *config);
diff --git a/res/res_features.c b/res/res_features.c
index afa77818a8edaa8f67a8f6e377fd180509d3db31..cbb59a9151b23234771d3c9c994e0ba4c7a0fc02 100644
--- a/res/res_features.c
+++ b/res/res_features.c
@@ -179,12 +179,12 @@ AST_MUTEX_DEFINE_STATIC(parking_lock);	/*!< protects all static variables above
 
 static pthread_t parking_thread;
 
-char *ast_parking_ext(void)
+const char *ast_parking_ext(void)
 {
 	return parking_ext;
 }
 
-char *ast_pickup_ext(void)
+const char *ast_pickup_ext(void)
 {
 	return pickup_ext;
 }
@@ -322,7 +322,7 @@ static int adsi_announce_park(struct ast_channel *chan, char *parkingexten)
 }
 
 /*! \brief Notify metermaids that we've changed an extension */
-static void notify_metermaids(char *exten, char *context)
+static void notify_metermaids(const char *exten, char *context)
 {
 	if (option_debug > 3)
 		ast_log(LOG_DEBUG, "Notification of state change to metermaids %s@%s\n", exten, context);