https://github.com/apple/swift-corelibs-libdispatch/pull/534

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2bae74e..0877f56 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -190,6 +190,8 @@ if(NOT CMAKE_SYSTEM_NAME STREQUAL Android)
   find_package(LibRT)
 endif()
 
+find_package(BlocksRuntime QUIET)
+
 check_function_exists(_pthread_workqueue_init HAVE__PTHREAD_WORKQUEUE_INIT)
 check_function_exists(getprogname HAVE_GETPROGNAME)
 check_function_exists(mach_absolute_time HAVE_MACH_ABSOLUTE_TIME)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 570c919..6d45899 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,5 +1,4 @@
-
-if(NOT CMAKE_SYSTEM_NAME STREQUAL Darwin)
+if(NOT BlocksRuntime_FOUND)
   add_subdirectory(BlocksRuntime)
 endif()
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 0176a06..523ae06 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -78,9 +78,6 @@ function(add_unit_test name)
     # to reduce probability of test failures due to machine load.
     target_compile_options(${name} PRIVATE -DLENIENT_DEADLINES=1)
   endif()
-  target_include_directories(${name}
-                             SYSTEM BEFORE PRIVATE
-                               "${BlocksRuntime_INCLUDE_DIR}")
   if("${CMAKE_C_SIMULATE_ID}" STREQUAL "MSVC")
     target_compile_options(${name} PRIVATE -Xclang -fblocks)
     target_compile_options(${name} PRIVATE /W3 -Wno-deprecated-declarations)