diff --git a/changes/sdk/pr.323.gh.OpenXR-SDK-Source.md b/changes/sdk/pr.323.gh.OpenXR-SDK-Source.md
new file mode 100644
index 000000000..b15bfab79
--- /dev/null
+++ b/changes/sdk/pr.323.gh.OpenXR-SDK-Source.md
@@ -0,0 +1 @@
+Loader: add -DXR_OS_APPLE define on macOS (fixes compilation on macOS)
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 3730546b9..3da42ae99 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -139,6 +139,8 @@ elseif(CMAKE_SYSTEM_NAME STREQUAL "Linux")
     add_definitions(-DXR_OS_LINUX)
 elseif(ANDROID)
     add_definitions(-DXR_OS_ANDROID)
+elseif(APPLE)
+    add_definitions(-DXR_OS_APPLE)
 endif()
 
 # /EHsc (support for C++ exceptions) is default in most configurations but seems missing when building arm/arm64.