diff --git a/README.md b/README.md
index 90a9c170391..4b0eb1f7347 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,7 @@ Cargo requires the following tools and packages to build:
 * `git`
 * `python`
 * `curl` (on Unix)
+* `pkg-config` (on Unix, used to figure out the `libssl` headers/libraries)
 * OpenSSL headers (only for Unix, this is the `libssl-dev` package on ubuntu)
 * `cargo` and `rustc`