diff --git a/callagent/SIPCallAgent.st b/callagent/SIPCallAgent.st
index 244b274..feb76a3 100644
--- a/callagent/SIPCallAgent.st
+++ b/callagent/SIPCallAgent.st
@@ -358,7 +358,8 @@ SIPUserAgentBase subclass: SIPUserAgent [
                     addParameter: 'From' value: dialog generateTo;
                     addParameter: 'To' value: dialog generateFrom;
                     addParameter: 'Call-ID' value: dialog callId;
-                    addParameter: 'CSeq' value: '%1 %2' % {cseq number. cseq method};
+                    addParameter: 'CSeq' value: ('<1p> <2s>'
+                                            expandMacrosWith: cseq with: cseq method);
                     addParameter: 'Allow' value: 'ACK,BYE';
                     yourself.
         self injectDefaults: resp.
diff --git a/callagent/SIPTransactions.st b/callagent/SIPTransactions.st
index c48f826..7c00361 100644
--- a/callagent/SIPTransactions.st
+++ b/callagent/SIPTransactions.st
@@ -259,7 +259,8 @@ Object subclass: SIPTransaction [
         invite := (SIPInviteRequest from: initial_dialog)
                         sdp: sdp;
                         addParameter: 'Via' value: (useragent generateVia: branch);
-                        addParameter: 'CSeq' value: '%1 %2' % {cseq. 'INVITE'};
+                        addParameter: 'CSeq' value: ('<1p> <2s>'
+                                            expandMacrosWith: cseq with: 'INVITE');
                         addParameter: 'Allow' value: 'ACK,BYE';
                         addParameter: 'Call-ID' value: initial_dialog callId;
                         yourself.
@@ -273,7 +274,8 @@ Object subclass: SIPTransaction [
 
         ack := (SIPACKRequest from: aDialog)
             addParameter: 'Via' value: (useragent generateVia: aBranch);
-            addParameter: 'CSeq' value: '%1 %2' % {cseq. 'ACK'};
+            addParameter: 'CSeq' value: ('<1p> <2s>'
+                                            expandMacrosWith: cseq with: 'ACK');
             addParameter: 'Call-ID' value: aDialog callId;
             yourself.
         useragent injectDefaults: ack.
@@ -286,7 +288,8 @@ Object subclass: SIPTransaction [
 
         bye := (SIPByeRequest from: aDialog)
                         addParameter: 'Via' value: (useragent generateVia: branch);
-                        addParameter: 'CSeq' value: '%1 %2' % {cseq. 'BYE'};
+                        addParameter: 'CSeq' value: ('<1p> <2s>'
+                                            expandMacrosWith: cseq with: 'BYE');
                         addParameter: 'Call-ID' value: aDialog callId;
                         yourself.
         useragent injectDefaults: bye.
@@ -299,7 +302,8 @@ Object subclass: SIPTransaction [
 
         cancel := (SIPCancelRequest from: initial_dialog)
                         addParameter: 'Via' value: (useragent generateVia: branch);
-                        addParameter: 'CSeq' value: '%1 %2' % {cseq. 'CANCEL'};
+                        addParameter: 'CSeq' value: ('<1p> <2s>'
+                                                expandMacrosWith: cseq with: 'CANCEL');
                         addParameter: 'Call-ID' value: initial_dialog callId;
                         yourself.
         useragent injectDefaults: cancel.