diff --git a/C/errors.c b/C/errors.c
index 89cf3f69e..cc3d4567e 100755
--- a/C/errors.c
+++ b/C/errors.c
@@ -530,7 +530,7 @@ Yap_bug_location(yamop *pc)
 static char tmpbuf[YAP_BUF_SIZE];
 
 yamop *
-Yap_NilError(yap_error_number type, char *format,...)
+Yap_NilError(yap_error_number type, const char *format,...)
 {
   va_list ap;
   yamop *res;
@@ -544,7 +544,7 @@ Yap_NilError(yap_error_number type, char *format,...)
 }
 
 yamop *
-Yap_Error(yap_error_number type, Term where, char *format,...)
+Yap_Error(yap_error_number type, Term where, const char *format,...)
 {
   CACHE_REGS
   va_list ap;
diff --git a/H/Yapproto.h b/H/Yapproto.h
index c22d53001..8b51c5b06 100755
--- a/H/Yapproto.h
+++ b/H/Yapproto.h
@@ -115,7 +115,7 @@ Int    YAP_Execute(struct pred_entry *, CPredicate);
 Int    YAP_ExecuteFirst(struct pred_entry *, CPredicate);
 Int    YAP_ExecuteNext(struct pred_entry *, CPredicate);
 Int    YAP_ExecuteOnCut(struct pred_entry *, CPredicate, struct cut_c_str *);
-Int    YAP_RunGoalOnce(Term);
+extern Int    Yap_RunGoalOnce(Term);
 #endif
 
 /* cdmgr.c */
@@ -167,8 +167,8 @@ Yap_PrintPredName( struct pred_entry  *ap );
 #endif
 void	Yap_RestartYap(int);
 void	Yap_exit(int);
-yamop  *Yap_Error(yap_error_number,Term,char *msg, ...);
-yamop  *Yap_NilError(yap_error_number,char *msg, ...);
+yamop  *Yap_Error(yap_error_number,Term, const char *msg, ...);
+yamop  *Yap_NilError(yap_error_number, const char *msg, ...);
 int     Yap_HandleError( const char *msg, ... );
 int     Yap_SWIHandleError( const char *, ... );