diff --git a/CMakeLists.txt b/CMakeLists.txt
index e3c67c55cd..4e427eea26 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -83,6 +83,8 @@ if(CMAKE_SYSTEM_NAME STREQUAL "Darwin")
 endif()
 
 if(WIN32 OR CMAKE_SYSTEM_NAME STREQUAL "Darwin")
+  # Ignore case when comparing filenames on Windows and Mac.
+  set(CASE_INSENSITIVE_FILENAME TRUE)
   # Enable fixing case-insensitive filenames for Windows and Mac.
   set(USE_FNAME_CASE TRUE)
 endif()
diff --git a/config/config.h.in b/config/config.h.in
index 95e2c872a3..275bff79a0 100644
--- a/config/config.h.in
+++ b/config/config.h.in
@@ -40,6 +40,7 @@
 #cmakedefine HAVE_WORKING_LIBINTL
 #cmakedefine HAVE_WSL
 #cmakedefine UNIX
+#cmakedefine CASE_INSENSITIVE_FILENAME
 #cmakedefine USE_FNAME_CASE
 #cmakedefine HAVE_SYS_UIO_H
 #ifdef HAVE_SYS_UIO_H