diff --git a/src/public/minbase/minbase_macros.h b/src/public/minbase/minbase_macros.h
index 0292535..efa2c5d 100644
--- a/src/public/minbase/minbase_macros.h
+++ b/src/public/minbase/minbase_macros.h
@@ -32,7 +32,7 @@
 // If available use static_assert instead of weird language tricks. This
 // leads to much more readable messages when compile time assert constraints
 // are violated.
-#if !defined(OSX) && (_MSC_VER > 1500 || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5) || defined(__clang__) )
+#if (_MSC_VER > 1500 || __GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 5) || defined(__clang__) )
 	#define PLAT_COMPILE_TIME_ASSERT( pred ) static_assert( pred, "Compile time assert constraint is not true: " #pred )
 #else
 	#define PLAT_COMPILE_TIME_ASSERT( pred ) typedef int UNIQUE_ID[ (pred) ? 1 : -1]
diff --git a/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp b/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
index 69e4050..fab97e8 100644
--- a/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
+++ b/src/steamnetworkingsockets/clientlib/csteamnetworkingsockets.cpp
@@ -425,7 +425,7 @@ bool CSteamNetworkingSockets::GetCertificateRequest( int *pcbBlob, void *pBlob,
 	}
 
 	// Check size
-	int cb = msgRequest.ByteSize();
+	ProtoMsgSize cb = msgRequest.ProtoByteSize();
 	if ( !pBlob )
 	{
 		*pcbBlob = cb;
diff --git a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.h b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.h
index b5c1fef..e59c72d 100644
--- a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.h
+++ b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_connections.h
@@ -97,13 +97,13 @@ struct SendPacketContext : SendPacketContext_t
 
 	uint32 m_nFlags; // Message flags that we need to set.
 	TStatsMsg msg; // Type-specific stats message
-	int m_cbMsgSize; // Size of message
-	int m_cbTotalSize; // Size needed in the header, including the serialized size field
+	ProtoMsgSize m_cbMsgSize; // Size of message
+	ProtoMsgSize m_cbTotalSize; // Size needed in the header, including the serialized size field
 
 	void SlamFlagsAndCalcSize()
 	{
 		SetStatsMsgFlagsIfNotImplied( msg, m_nFlags );
-		m_cbTotalSize = m_cbMsgSize = msg.ByteSize();
+		m_cbTotalSize = m_cbMsgSize = msg.ProtoByteSize();
 		if ( m_cbMsgSize > 0 )
 			m_cbTotalSize += VarIntSerializedSize( (uint32)m_cbMsgSize );
 	}
diff --git a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_udp.cpp b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_udp.cpp
index 8a91703..2c0a483 100644
--- a/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_udp.cpp
+++ b/src/steamnetworkingsockets/clientlib/steamnetworkingsockets_udp.cpp
@@ -492,10 +492,10 @@ void CSteamNetworkListenSocketDirectUDP::SendMsg( uint8 nMsgID, const google::pr
 
 	uint8 pkt[ k_cbSteamNetworkingSocketsMaxUDPMsgLen ];
 	pkt[0] = nMsgID;
-	int cbPkt = msg.ByteSize()+1;
+	ProtoMsgSize cbPkt = msg.ProtoByteSize()+1;
 	if ( cbPkt > sizeof(pkt) )
 	{
-		AssertMsg3( false, "Msg type %d is %d bytes, larger than MTU of %d bytes", int( nMsgID ), cbPkt, (int)sizeof(pkt) );
+		AssertMsg3( false, "Msg type %d is %d bytes, larger than MTU of %d bytes", int( nMsgID ), int( cbPkt ), (int)sizeof(pkt) );
 		return;
 	}
 	uint8 *pEnd = msg.SerializeWithCachedSizesToArray( pkt+1 );
@@ -511,7 +511,7 @@ void CSteamNetworkListenSocketDirectUDP::SendPaddedMsg( uint8 nMsgID, const goog
 	uint8 pkt[ k_cbSteamNetworkingSocketsMaxUDPMsgLen ];
 	memset( pkt, 0, sizeof(pkt) ); // don't send random bits from our process memory over the wire!
 	UDPPaddedMessageHdr *hdr = (UDPPaddedMessageHdr *)pkt;
-	int nMsgLength = msg.ByteSize();
+	ProtoMsgSize nMsgLength = msg.ProtoByteSize();
 	hdr->m_nMsgID = nMsgID;
 	hdr->m_nMsgLength = LittleWord( uint16( nMsgLength ) );
 	uint8 *pEnd = msg.SerializeWithCachedSizesToArray( pkt + sizeof(*hdr) );
@@ -1017,10 +1017,10 @@ void CConnectionTransportUDP::SendMsg( uint8 nMsgID, const google::protobuf::Mes
 
 	uint8 pkt[ k_cbSteamNetworkingSocketsMaxUDPMsgLen ];
 	pkt[0] = nMsgID;
-	int cbPkt = msg.ByteSize()+1;
+	ProtoMsgSize cbPkt = msg.ProtoByteSize()+1;
 	if ( cbPkt > sizeof(pkt) )
 	{
-		AssertMsg3( false, "Msg type %d is %d bytes, larger than MTU of %d bytes", int( nMsgID ), cbPkt, (int)sizeof(pkt) );
+		AssertMsg3( false, "Msg type %d is %d bytes, larger than MTU of %d bytes", int( nMsgID ), int( cbPkt ), (int)sizeof(pkt) );
 		return;
 	}
 	uint8 *pEnd = msg.SerializeWithCachedSizesToArray( pkt+1 );
@@ -1035,7 +1035,7 @@ void CConnectionTransportUDP::SendPaddedMsg( uint8 nMsgID, const google::protobu
 	uint8 pkt[ k_cbSteamNetworkingSocketsMaxUDPMsgLen ];
 	V_memset( pkt, 0, sizeof(pkt) ); // don't send random bits from our process memory over the wire!
 	UDPPaddedMessageHdr *hdr = (UDPPaddedMessageHdr *)pkt;
-	int nMsgLength = msg.ByteSize();
+	ProtoMsgSize nMsgLength = msg.ProtoByteSize();
 	if ( nMsgLength + sizeof(*hdr) > k_cbSteamNetworkingSocketsMaxUDPMsgLen )
 	{
 		AssertMsg3( false, "Msg type %d is %d bytes, larger than MTU of %d bytes", int( nMsgID ), int( nMsgLength + sizeof(*hdr) ), (int)sizeof(pkt) );
diff --git a/src/steamnetworkingsockets/steamnetworkingsockets_certs.cpp b/src/steamnetworkingsockets/steamnetworkingsockets_certs.cpp
index 0dc6c60..3ffc686 100644
--- a/src/steamnetworkingsockets/steamnetworkingsockets_certs.cpp
+++ b/src/steamnetworkingsockets/steamnetworkingsockets_certs.cpp
@@ -93,7 +93,7 @@ bool BSteamNetworkingIdentityFromLegacyBinaryProtobuf( SteamNetworkingIdentity &
 	{
 		V_sprintf_safe( errMsg, "Unrecognized identity format.  (%d unknown field(s), first ID=%d)", msgIdentity.unknown_fields().field_count(), msgIdentity.unknown_fields().field(0).number() );
 	}
-	else if ( msgIdentity.ByteSize() == 0 )
+	else if ( msgIdentity.ProtoByteSize() == 0 )
 	{
 		V_strcpy_safe( errMsg, "Empty identity msg" );
 	}
diff --git a/src/steamnetworkingsockets/steamnetworkingsockets_internal.h b/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
index 1f05742..e5d9bb5 100644
--- a/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
+++ b/src/steamnetworkingsockets/steamnetworkingsockets_internal.h
@@ -110,6 +110,14 @@ struct iovec;
 // Internal stuff goes in a private namespace
 namespace SteamNetworkingSocketsLib {
 
+#if GOOGLE_PROTOBUF_VERSION < 3004000
+using ProtoMsgSize = int;
+#define ProtoByteSize ByteSize
+#else
+using ProtoMsgSize = size_t;
+#define ProtoByteSize ByteSizeLong
+#endif
+
 struct SteamDatagramLinkStats;
 struct SteamDatagramLinkLifetimeStats;
 struct SteamDatagramLinkInstantaneousStats;