diff --git a/C/iopreds.c b/C/iopreds.c
index c01b52907..c40145f7d 100644
--- a/C/iopreds.c
+++ b/C/iopreds.c
@@ -5953,10 +5953,9 @@ p_format(void)
   return res;
 }
 
-
 static Int
-p_format2(void)
-{				/* 'format'(Stream,Control,Args)          */
+format2(UInt  stream_flag)
+{
   int old_c_stream = Yap_c_output_stream;
   int mem_stream = FALSE, codes_stream = FALSE;
   Int out;
@@ -5975,7 +5974,7 @@ p_format2(void)
     mem_stream = TRUE;
   } else {
     /* needs to change Yap_c_output_stream for write */
-    Yap_c_output_stream = CheckStream (ARG1, Output_Stream_f, "format/3");
+    Yap_c_output_stream = CheckStream (ARG1, Output_Stream_f|stream_flag, "format/3");
   }
   UNLOCK(Stream[Yap_c_output_stream].streamlock);
   if (Yap_c_output_stream == -1) {
@@ -6007,6 +6006,18 @@ p_format2(void)
   return out;
 }
 
+static Int
+p_format2(void)
+{				/* 'format'(Stream,Control,Args)          */
+  return format2(0);
+}
+
+static Int
+p_swi_format(void)
+{				/* 'format'(Stream,Control,Args)          */
+  return format2(SWI_Stream_f);
+}
+
 
 static Int
 p_skip (void)
@@ -6804,6 +6815,10 @@ Yap_InitIOPreds(void)
   Yap_InitCPred ("$tolower", 2, p_tolower, SafePredFlag|HiddenPredFlag);
   Yap_InitCPred ("file_base_name", 2, p_file_base_name, SafePredFlag|HiddenPredFlag);
 
+  CurrentModule = SYSTEM_MODULE;
+  Yap_InitCPred ("swi_format", 3, p_swi_format, SyncPredFlag);
+  CurrentModule = cm;
+
   Yap_InitReadUtil ();
 #if USE_SOCKET
   Yap_InitSockets ();
diff --git a/library/dialect/swi.yap b/library/dialect/swi.yap
index 159acaa5a..b460203dd 100755
--- a/library/dialect/swi.yap
+++ b/library/dialect/swi.yap
@@ -242,6 +242,9 @@ goal_expansion(print(A),write_term(user_output,A,[swi(true),portray(true),number
 goal_expansion(print(S,A),write_term(S,A,[swi(true),portray(true),numbervars(true)])) :- swi_io.
 goal_expansion(write_term(A,Opts),write_term(user_output,A,Opts,[swi(true)|Opts])) :- swi_io.
 goal_expansion(write_term(S,A,Opts),write_term(S,A,[swi(true)|Opts])) :- swi_io, \+ member(swi(_), Opts).
+goal_expansion(format(A),system:swi_format(user_output,A,[])) :- swi_io.
+goal_expansion(format(A,Args),system:swi_format(user_output,A,Args)) :- swi_io.
+goal_expansion(format(S,A,Args),system:swi_format(S,A,Args)) :- swi_io.
 
 
 % make sure we also use