diff --git a/CMakeLists.txt b/CMakeLists.txt
index f3e69b845..12fb2188d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -66,12 +66,14 @@ option(EIGEN_TEST_CXX11 "Enable testing with C++11 and C++11 features (e.g. Tens
 
 
 macro(ei_add_cxx_compiler_flag FLAG)
+  if(FALSE) # Since eigen3 is header only and vcpkg does not build tests this can be disabled by default. 
   string(REGEX REPLACE "-" "" SFLAG1 ${FLAG})
   string(REGEX REPLACE "\\+" "p" SFLAG ${SFLAG1})
   check_cxx_compiler_flag(${FLAG} COMPILER_SUPPORT_${SFLAG})
   if(COMPILER_SUPPORT_${SFLAG})
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${FLAG}")
   endif()
+  endif()
 endmacro()
 
 check_cxx_compiler_flag("-std=c++11" EIGEN_COMPILER_SUPPORT_CPP11)
@@ -142,7 +144,7 @@ endif()
 
 set(EIGEN_TEST_MAX_SIZE "320" CACHE STRING "Maximal matrix/vector size, default is 320")
 
-if(NOT MSVC)
+if(NOT MSVC AND FALSE)
   # We assume that other compilers are partly compatible with GNUCC
 
   # clang outputs some warnings for unknown flags that are not caught by check_cxx_compiler_flag
@@ -330,7 +332,7 @@ if(NOT MSVC)
     endif()
   endif()
 
-else()
+elseif(FALSE)
 
   # C4127 - conditional expression is constant
   # C4714 - marked as __forceinline not inlined (I failed to deactivate it selectively)