diff --git a/src/librustc_target/spec/apple_ios_base.rs b/src/librustc_target/spec/apple_ios_base.rs
index d400bc62bfd07..f46ad06ba436a 100644
--- a/src/librustc_target/spec/apple_ios_base.rs
+++ b/src/librustc_target/spec/apple_ios_base.rs
@@ -29,6 +29,12 @@ impl Arch {
 }
 
 pub fn get_sdk_root(sdk_name: &str) -> Result<String, String> {
+    // Following what clang does
+    // (https://github.com/llvm/llvm-project/blob/
+    // 296a80102a9b72c3eda80558fb78a3ed8849b341/clang/lib/Driver/ToolChains/Darwin.cpp#L1661-L1678)
+    // to allow the SDK path to be set. (For clang, xcrun sets
+    // SDKROOT; for rustc, the user or build system can set it, or we
+    // can fall back to checking for xcrun on PATH.)
     if let Some(sdkroot) = env::var("SDKROOT").ok() {
         let sdkroot_path = Path::new(&sdkroot);
         if sdkroot_path.is_absolute() && sdkroot_path != Path::new("/") && sdkroot_path.exists() {