diff --git a/src/doc/unstable-book/src/compiler-flags/sanitizer.md b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
index c15f339783f7e..93908e9190e64 100644
--- a/src/doc/unstable-book/src/compiler-flags/sanitizer.md
+++ b/src/doc/unstable-book/src/compiler-flags/sanitizer.md
@@ -26,6 +26,9 @@ of bugs:
 * Double-free, invalid free
 * Memory leaks
 
+The memory leak detection is enabled by default on Linux, and can be enabled
+with runtime flag `ASAN_OPTIONS=detect_leaks=1` on macOS.
+
 AddressSanitizer is supported on the following targets:
 
 * `x86_64-apple-darwin`