diff --git a/.appveyor.yml b/.appveyor.yml
index 96fd20813e..cfb0325a80 100644
--- a/.appveyor.yml
+++ b/.appveyor.yml
@@ -15,7 +15,13 @@ install:
 build_script:
   - call "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\VC\Auxiliary\Build\vcvars64.bat"
   - cd %APPVEYOR_BUILD_FOLDER% && mkdir build && cd build
-  - if %CFG% == MSVC (cmake ../src -DCMAKE_BUILD_TYPE=Release -DCMAKE_TOOLCHAIN_FILE=c:/tools/vcpkg/scripts/buildsystems/vcpkg.cmake -G "NMake Makefiles" &&
+  # disable slow LTO
+  - if %CFG% == MSVC (cmake ../src
+      -DCMAKE_BUILD_TYPE=Release
+      -DCMAKE_TOOLCHAIN_FILE=c:/tools/vcpkg/scripts/buildsystems/vcpkg.cmake
+      -DLEAN_EXTRA_CXX_FLAGS=/GL-
+      -DLEAN_EXTRA_LINKER_FLAGS_MSVC=/LTCG:OFF
+      -G "NMake Makefiles" &&
       cmake --build .)
   - if %CFG% == MINGW64 (C:\msys64\usr\bin\bash -lc "exec 0</dev/null && cd $APPVEYOR_BUILD_FOLDER/build &&
       OPTIONS='';
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 22d532e6d5..aa28fe1dc2 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -9,8 +9,8 @@ set(LEAN_VERSION_PATCH 1)
 set(LEAN_VERSION_IS_RELEASE 0)  # This number is 1 in the release revision, and 0 otherwise.
 set(LEAN_VERSION_STRING "${LEAN_VERSION_MAJOR}.${LEAN_VERSION_MINOR}.${LEAN_VERSION_PATCH}" CACHE STRING "Lean version string")
 
-set(LEAN_EXTRA_LINKER_FLAGS "")
-set(LEAN_EXTRA_CXX_FLAGS "")
+set(LEAN_EXTRA_LINKER_FLAGS "" CACHE STRING "Additional flags used by the linker")
+set(LEAN_EXTRA_CXX_FLAGS "" CACHE STRING "Additional flags used by the C++ compiler")
 
 if (NOT CMAKE_BUILD_TYPE)
   message(STATUS "No build type selected, default to Release")
@@ -253,8 +253,8 @@ elseif (MSVC)
     set(CMAKE_CXX_FLAGS_MINSIZEREL     "/Os /Zc:inline ${CMAKE_CXX_FLAGS_MINSIZEREL}")
     set(CMAKE_CXX_FLAGS_RELEASE        "/O2 /Oi /Oy /Zc:inline ${CMAKE_CXX_FLAGS_RELEASE}")
     set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "/O2 /Oi /Zi ${CMAKE_CXX_FLAGS_RELWITHDEBINFO}")
-    set(LEAN_EXTRA_LINKER_FLAGS        "${LEAN_EXTRA_LINKER_FLAGS} /LTCG:INCREMENTAL")
-    set(CMAKE_STATIC_LINKER_FLAGS      "${CMAKE_STATIC_LINKER_FLAGS} /LTCG:INCREMENTAL")
+    set(LEAN_EXTRA_LINKER_FLAGS        "/LTCG:INCREMENTAL ${LEAN_EXTRA_LINKER_FLAGS}")
+    set(CMAKE_STATIC_LINKER_FLAGS      "${CMAKE_STATIC_LINKER_FLAGS} ${LEAN_EXTRA_LINKER_FLAGS}")
 elseif (EMSCRIPTEN)
     message(STATUS "Emscripten is detected: Make sure the wraped compiler supports C++11")
 else()