diff --git a/src/unsafe/mutable-static-variables.md b/src/unsafe/mutable-static-variables.md
index 75cf49e3..6383a2f3 100644
--- a/src/unsafe/mutable-static-variables.md
+++ b/src/unsafe/mutable-static-variables.md
@@ -29,7 +29,11 @@ fn main() {
 
 <details>
 
-Using a mutable static is generally a bad idea, but there are some cases where it might make sense
-in low-level `no_std` code, such as implementing a heap allocator or working with some C APIs.
+- The program here is safe because it is single-threaded. However, the Rust compiler is conservative
+  and will assume the worst. Try removing the `unsafe` and see how the compiler explains that it is
+  undefined behavior to mutate a static from multiple threads.
+
+- Using a mutable static is generally a bad idea, but there are some cases where it might make sense
+  in low-level `no_std` code, such as implementing a heap allocator or working with some C APIs.
 
 </details>