diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 1c7b03e..368ce75 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -1,12 +1,11 @@
 cmake_minimum_required(VERSION 3.0.2)
 
 project(GSLTests CXX)
+enable_testing()  # again, for support standalone testing
 
 include(FindPkgConfig)
 include(ExternalProject)
 
-find_package(Git REQUIRED QUIET)
-
 # will make visual studio generated project group files
 set_property(GLOBAL PROPERTY USE_FOLDERS ON)
 
@@ -16,6 +15,9 @@ endif()
 
 pkg_search_module(GTestMain gtest_main)
 if (NOT GTestMain_FOUND)
+    # No pre-installed GTest is available, try to download it using Git.
+    find_package(Git REQUIRED QUIET)
+
     configure_file(CMakeLists.txt.in googletest-download/CMakeLists.txt)
     execute_process(
         COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
@@ -45,6 +47,13 @@ if (NOT GTestMain_FOUND)
     )
 endif()
 
+if (CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
+    # CMake has been started independently in this directory with tests. Do
+    # import the globally installed Guidelines Support Library and test it
+    # instead of the current version from the include/ folder.
+    find_package(Microsoft.GSL REQUIRED)
+endif()
+
 if (MSVC AND (GSL_CXX_STANDARD EQUAL 17))
     set(GSL_CPLUSPLUS_OPT -Zc:__cplusplus -permissive-)
 endif()
@@ -160,7 +169,7 @@ set_property(TARGET  PROPERTY FOLDER "GSL_tests")
 function(add_gsl_test name)
     add_executable(${name} ${name}.cpp)
     target_link_libraries(${name}
-        GSL
+        Microsoft.GSL::GSL
         gsl_tests_config
         ${GTestMain_LIBRARIES}
     )
@@ -262,7 +271,7 @@ endif(MSVC)
 function(add_gsl_test_noexcept name)
     add_executable(${name} ${name}.cpp)
     target_link_libraries(${name}
-        GSL
+        Microsoft.GSL::GSL
         gsl_tests_config_noexcept
         ${GTestMain_LIBRARIES}
     )