diff --git a/core/AmMimeBody.cpp b/core/AmMimeBody.cpp
index 164f9b7a..e0a13cd9 100644
--- a/core/AmMimeBody.cpp
+++ b/core/AmMimeBody.cpp
@@ -481,8 +481,8 @@ int AmMimeBody::findNextBoundary(unsigned char** beg, unsigned char** end)
 int AmMimeBody::parseSinglePart(unsigned char* buf, unsigned int len)
 {
   list<sip_header*> hdrs;
-  char* c = (char*)buf;
-  char* end = c + len;
+  const char* c = (char*)buf;
+  const char* end = c + len;
 
   // parse headers first
   if(parse_headers(hdrs,&c,c+len) < 0) {
diff --git a/core/SipCtrlInterface.cpp b/core/SipCtrlInterface.cpp
index 2d43c780..60094e8d 100644
--- a/core/SipCtrlInterface.cpp
+++ b/core/SipCtrlInterface.cpp
@@ -244,10 +244,10 @@ int SipCtrlInterface::send(AmSipRequest &req, const string& dialog_id,
      * Contact
      * Max-Forwards */
     
-    char * c = (char*)req.from.c_str();
+    const char* c = req.from.c_str();
     int err = parse_headers(msg, &c, (c + req.from.length()));
 
-    c = (char*)req.to.c_str();
+    c = req.to.c_str();
     err = err || parse_headers(msg, &c, (c + req.to.length()));
 
     if (err) {
@@ -373,7 +373,7 @@ int SipCtrlInterface::send(const AmSipReply &rep, const string& dialog_id,
 
     if(!rep.hdrs.empty()) {
 
-	char* c = (char*)rep.hdrs.c_str();
+	const char* c = rep.hdrs.c_str();
 	int err = parse_headers(&msg,&c,c+rep.hdrs.length());
 	if(err){
 	    ERROR("Malformed additional header\n");
@@ -383,7 +383,7 @@ int SipCtrlInterface::send(const AmSipReply &rep, const string& dialog_id,
 
     if(!rep.contact.empty()){
 
-	char* c = (char*)rep.contact.c_str();
+	const char* c = rep.contact.c_str();
 	int err = parse_headers(&msg,&c,c+rep.contact.length());
 	if(err){
 	    ERROR("Malformed Contact header\n");
diff --git a/core/sip/parse_header.cpp b/core/sip/parse_header.cpp
index 7730b5a5..70d22b09 100644
--- a/core/sip/parse_header.cpp
+++ b/core/sip/parse_header.cpp
@@ -268,7 +268,7 @@ void add_parsed_header(list<sip_header*>& hdrs, sip_header* hdr)
     hdrs.push_back(hdr);
 }
 
-int parse_headers(list<sip_header*>& hdrs, char** c, char* end)
+int parse_headers(list<sip_header*>& hdrs, const char** c, const char* end)
 {
     //
     // Header states
@@ -283,7 +283,7 @@ int parse_headers(list<sip_header*>& hdrs, char** c, char* end)
     int st = H_NAME;
     int saved_st = 0;
 
-    char* begin = *c;
+    const char* begin = *c;
     if(!(*c) || (*c == end)) {
 	return 0;
     }
diff --git a/core/sip/parse_header.h b/core/sip/parse_header.h
index 701044c2..59a2f94b 100644
--- a/core/sip/parse_header.h
+++ b/core/sip/parse_header.h
@@ -82,7 +82,7 @@ struct sip_header
 
 int parse_header_type(sip_header* h);
 
-int parse_headers(list<sip_header*>& hdrs, char** c, char* end);
+int parse_headers(list<sip_header*>& hdrs, const char** c, const char* end);
 void free_headers(list<sip_header*>& hdrs);
 
 #endif
diff --git a/core/sip/sip_parser.cpp b/core/sip/sip_parser.cpp
index b3849dd9..bbf9dd27 100644
--- a/core/sip/sip_parser.cpp
+++ b/core/sip/sip_parser.cpp
@@ -241,7 +241,7 @@ int parse_method(int* method, const char* beg, int len)
 }
 
 
-static int parse_first_line(sip_msg* msg, char** c, char* end)
+static int parse_first_line(sip_msg* msg, const char** c, const char* end)
 {
     enum {
 	FL_METH=0,
@@ -267,7 +267,7 @@ static int parse_first_line(sip_msg* msg, char** c, char* end)
 	FL_ERR
     };
 
-    char* beg = *c;
+    const char* beg = *c;
     int saved_st=0, st=FL_SIPVER1;
     int err=0;
 
@@ -454,7 +454,7 @@ static int parse_first_line(sip_msg* msg, char** c, char* end)
     return UNEXPECTED_EOT;
 }
 
-int parse_headers(sip_msg* msg, char** c, char* end)
+int parse_headers(sip_msg* msg, const char** c, const char* end)
 {
     list<sip_header*> hdrs;
     int err = parse_headers(hdrs,c,end);
@@ -528,8 +528,8 @@ int parse_headers(sip_msg* msg, char** c, char* end)
 
 int parse_sip_msg(sip_msg* msg, char*& err_msg)
 {
-    char* c = msg->buf;
-    char* end = msg->buf + msg->len;
+    const char* c = msg->buf;
+    const char* end = c + msg->len;
 
     int err = parse_first_line(msg,&c,end);
 
diff --git a/core/sip/sip_parser.h b/core/sip/sip_parser.h
index d8da66f1..559af47f 100644
--- a/core/sip/sip_parser.h
+++ b/core/sip/sip_parser.h
@@ -156,7 +156,7 @@ struct sip_msg
 };
 
 int parse_method(int* method, const char* beg, int len);
-int parse_headers(sip_msg* msg, char** c, char* end);
+int parse_headers(sip_msg* msg, const char** c, const char* end);
 int parse_sip_msg(sip_msg* msg, char*& err_msg);
 
 #define get_contact(msg) (msg->contacts.empty() ? NULL : (*msg->contacts.begin()))
diff --git a/core/sip/trans_layer.cpp b/core/sip/trans_layer.cpp
index 34bc555c..dfe2cc58 100644
--- a/core/sip/trans_layer.cpp
+++ b/core/sip/trans_layer.cpp
@@ -654,7 +654,7 @@ int trans_layer::send_sf_error_reply(const trans_ticket* tt, const sip_msg* req,
     sip_msg reply;
     reply.u.reply = new sip_reply(reply_code,reason);
 
-    char* c = (char*)hdrs.s;
+    const char* c = hdrs.s;
     int err = parse_headers(&reply,&c,c+hdrs.len);
     if(err){
 	ERROR("Malformed additional header\n");