diff --git a/windows/readme.md b/windows/readme.md
index 411eba0..8957fbd 100644
--- a/windows/readme.md
+++ b/windows/readme.md
@@ -3,7 +3,7 @@
 ## Configure Shell
 * Install [MSYS2 w/ MinGW-w64](http://www.msys2.org/) to `C:\msys64`
   * Open `C:\msys64\mingw64.exe`
-  * Run `pacman -S base-devel mingw-w64-x86_64-toolchain git`
+  * Run `pacman -S base-devel mingw-w64-x86_64-toolchain git bc`
   * Use `C:\Users\<user>` as the terminal $HOME by editting `C:\msys64\etc\nsswitch.conf` and
     changing the `db_home` value to `windows`.
 * You may need to work around an issue with envsubst.exe - you'll know there's a bug if git