diff --git a/README.md b/README.md
index 7cd802762b..0c5b591e72 100644
--- a/README.md
+++ b/README.md
@@ -59,6 +59,9 @@ in your program, and cannot run all programs:
   has no access to most platform-specific APIs or FFI. A few APIs have been
   implemented (such as printing to stdout) but most have not: for example, Miri
   currently does not support SIMD or networking.
+* Threading support is not finished yet. E.g., weak memory effects are not
+  emulated and spin loops (without syscalls) just loop forever. There is no
+  threading support on Windows.
 
 [rust]: https://www.rust-lang.org/
 [mir]: https://github.com/rust-lang/rfcs/blob/master/text/1211-mir.md