diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0d754eb5..e025342a 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -54,6 +54,16 @@ if(CMAKE_SIZEOF_VOID_P EQUAL 8)
 	endif()
 endif()
 
+# add_compile_options for older cmake versions
+if(${CMAKE_VERSION} VERSION_LESS "3.0.2")
+macro(add_compile_options)
+	set(list_var "${ARGV}")
+	foreach(arg IN LISTS list_var)
+		set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${arg}")
+	endforeach()
+endmacro()
+endif()
+
 if(BUILD_CLIENT)
 	add_subdirectory(cl_dll)
 endif()
diff --git a/dlls/CMakeLists.txt b/dlls/CMakeLists.txt
index bf65b00f..bf7d3370 100644
--- a/dlls/CMakeLists.txt
+++ b/dlls/CMakeLists.txt
@@ -29,6 +29,7 @@ add_definitions(-DCLIENT_WEAPONS)
 
 if(NOT MSVC)
 	add_compile_options(-fno-exceptions) # GCC/Clang flag
+	add_compile_options(-Wno-invalid-offsetof) # GCC/Clang flag
 	add_definitions(-D_LINUX) # It seems enough for all non-Win32 systems
 	add_definitions(-Dstricmp=strcasecmp -Dstrnicmp=strncasecmp -D_snprintf=snprintf -D_vsnprintf=vsnprintf )
 else()
diff --git a/dlls/playermonster.cpp b/dlls/playermonster.cpp
index cd3484ab..a6e38389 100644
--- a/dlls/playermonster.cpp
+++ b/dlls/playermonster.cpp
@@ -1,4 +1,4 @@
-//========= Copyright © 1996-2002, Valve LLC, All rights reserved. ============
+//========= Copyright © 1996-2002, Valve LLC, All rights reserved. ============
 //
 // Purpose: New version of the slider bar
 //
@@ -82,7 +82,7 @@ void CPlayerMonster :: HandleAnimEvent( MonsterEvent_t *pEvent )
 //=========================================================
 int CPlayerMonster::ISoundMask( void )
 {
-	return NULL;
+	return 0;
 }
 
 //=========================================================
diff --git a/utils/false_vgui/include/VGUI_Panel.h b/utils/false_vgui/include/VGUI_Panel.h
index bec7ac25..351b2375 100644
--- a/utils/false_vgui/include/VGUI_Panel.h
+++ b/utils/false_vgui/include/VGUI_Panel.h
@@ -219,7 +219,6 @@ private:
 	bool                _paintBorderEnabled;
 	bool                _paintBackgroundEnabled;
 	bool                _paintEnabled;
-friend class Panel;
 friend class App;
 friend class SurfaceBase;
 friend class Image;