diff --git a/CMakeLists.txt b/CMakeLists.txt
index 13ff7b1c..246d11a1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -363,6 +363,7 @@ if(ENABLE_THREADS)
     find_package(Threads REQUIRED)
 
     # If both Windows and posix threading are available, prefer Windows.
+    # Note that on Cygwin CMAKE_USE_WIN32_THREADS_INIT is false.
     if(CMAKE_USE_WIN32_THREADS_INIT AND NOT ENABLE_THREADS STREQUAL "posix")
         if(ENABLE_THREADS STREQUAL "win95"
                 OR (ENABLE_THREADS STREQUAL "ON"