diff --git a/extern/oics/CMakeLists.txt b/extern/oics/CMakeLists.txt
index 0f19dd8541..e9e08993dd 100644
--- a/extern/oics/CMakeLists.txt
+++ b/extern/oics/CMakeLists.txt
@@ -13,7 +13,7 @@ add_library(oics STATIC
     include/oics/ICSPrerequisites.h
 )
 
-target_include_directories(oics PUBLIC include)
+target_include_directories(oics SYSTEM PUBLIC include)
 target_include_directories(oics PRIVATE include/oics)
 
 if(USE_SYSTEM_TINYXML)
@@ -25,7 +25,7 @@ else()
         tinyxml/tinyxmlerror.cpp
         tinyxml/tinystr.cpp
     )
-    target_include_directories(local_tinyxml PUBLIC tinyxml)
+    target_include_directories(local_tinyxml SYSTEM PUBLIC tinyxml)
     target_link_libraries(oics local_tinyxml)
 endif()
 
diff --git a/extern/osg-ffmpeg-videoplayer/CMakeLists.txt b/extern/osg-ffmpeg-videoplayer/CMakeLists.txt
index 3b3ff0184d..ce20e95af2 100644
--- a/extern/osg-ffmpeg-videoplayer/CMakeLists.txt
+++ b/extern/osg-ffmpeg-videoplayer/CMakeLists.txt
@@ -20,7 +20,7 @@ target_link_libraries(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} ${FFmpeg_LIBRARIES})
 target_link_libraries(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} ${OSG_LIBRARIES})
 target_link_libraries(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} SDL2::SDL2)
 
-target_include_directories(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} PUBLIC include ${FFmpeg_INCLUDE_DIRS})
+target_include_directories(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} SYSTEM PUBLIC include ${FFmpeg_INCLUDE_DIRS})
 target_include_directories(${OSG_FFMPEG_VIDEOPLAYER_LIBRARY} PRIVATE include/osg-ffmpeg-videoplayer)
 
 if (MSVC AND PRECOMPILE_HEADERS_WITH_MSVC)
diff --git a/extern/osgQt/CMakeLists.txt b/extern/osgQt/CMakeLists.txt
index 3b7be3e042..32d0142106 100644
--- a/extern/osgQt/CMakeLists.txt
+++ b/extern/osgQt/CMakeLists.txt
@@ -16,7 +16,7 @@ set(OSGQT_SOURCE_FILES
 )
 
 add_library(${OSGQT_LIBRARY} STATIC ${OSGQT_SOURCE_FILES})
-target_include_directories(${OSGQT_LIBRARY} PUBLIC include)
+target_include_directories(${OSGQT_LIBRARY} SYSTEM PUBLIC include)
 target_include_directories(${OSGQT_LIBRARY} PRIVATE include/osgQt)
 
 target_link_libraries(${OSGQT_LIBRARY} Qt::Core Qt::OpenGL Qt::OpenGLWidgets)
diff --git a/extern/smhasher/CMakeLists.txt b/extern/smhasher/CMakeLists.txt
index cf4208ede6..b92f09e53d 100644
--- a/extern/smhasher/CMakeLists.txt
+++ b/extern/smhasher/CMakeLists.txt
@@ -1,3 +1,3 @@
 add_library(smhasher STATIC MurmurHash3.cpp include/smhasher/MurmurHash3.h)
-target_include_directories(smhasher PUBLIC include)
+target_include_directories(smhasher SYSTEM PUBLIC include)
 target_include_directories(smhasher PRIVATE include/smhasher)