diff --git a/core/AmAudio.h b/core/AmAudio.h
index b377bbed..b9ce7634 100644
--- a/core/AmAudio.h
+++ b/core/AmAudio.h
@@ -49,8 +49,8 @@ using std::string;
 
 #define SYSTEM_SAMPLERATE 8000 // fixme: sr per session
 
-class SdpPayload;
-class CodecContainer;
+struct SdpPayload;
+struct CodecContainer;
 
 /** \brief Audio Event */
 class AmAudioEvent: public AmEvent
diff --git a/core/AmRtpStream.h b/core/AmRtpStream.h
index 76afa84e..497a6213 100644
--- a/core/AmRtpStream.h
+++ b/core/AmRtpStream.h
@@ -58,7 +58,7 @@ struct amci_payload_t;
 
 class AmAudio;
 class AmSession;
-class SdpPayload;
+struct SdpPayload;
 typedef std::map<unsigned int, AmRtpPacket*, ts_less> ReceiveBuffer;
 typedef std::queue<AmRtpPacket*>  RtpEventQueue;
 
diff --git a/core/hash_table.h b/core/hash_table.h
index 468b0924..7a59d5d7 100644
--- a/core/hash_table.h
+++ b/core/hash_table.h
@@ -39,7 +39,7 @@
 using std::list;
 using std::map;
 
-struct sip_trans;
+class sip_trans;
 struct sip_msg;
 
 
diff --git a/core/sip/sip_parser.h b/core/sip/sip_parser.h
index 05d3b306..2b8cc5eb 100644
--- a/core/sip/sip_parser.h
+++ b/core/sip/sip_parser.h
@@ -45,7 +45,7 @@ struct sip_reply;
 struct sip_header;
 struct sip_via_parm;
 struct dns_handle;
-struct trsp_socket;
+class trsp_socket;
 
 //
 // SIP message types:
diff --git a/core/sip/sip_trans.h b/core/sip/sip_trans.h
index d2d2df67..5ffd895d 100644
--- a/core/sip/sip_trans.h
+++ b/core/sip/sip_trans.h
@@ -35,7 +35,7 @@
 #include <sys/socket.h>
 
 struct sip_msg;
-struct trsp_socket;
+class trsp_socket;
 
 /**
  * Transaction types
diff --git a/core/sip/trans_layer.h b/core/sip/trans_layer.h
index 17cbce9b..e5d72a2d 100644
--- a/core/sip/trans_layer.h
+++ b/core/sip/trans_layer.h
@@ -40,7 +40,7 @@ using std::vector;
 
 struct sip_msg;
 struct sip_uri;
-struct sip_trans;
+class sip_trans;
 struct sip_header;
 struct sockaddr_storage;
 
diff --git a/core/sip/wheeltimer.h b/core/sip/wheeltimer.h
index fb00a491..6f1087b7 100644
--- a/core/sip/wheeltimer.h
+++ b/core/sip/wheeltimer.h
@@ -43,7 +43,7 @@
 // do not change
 #define WHEELS 4
 
-struct timer;
+class timer;
 typedef void (*timer_cb)(timer*,unsigned int /*data1*/,void* /*data2*/);
 
 class base_timer