diff --git a/pills/15-nix-search-paths.xml b/pills/15-nix-search-paths.xml
index bf8345f..bc8fb21 100644
--- a/pills/15-nix-search-paths.xml
+++ b/pills/15-nix-search-paths.xml
@@ -105,7 +105,7 @@
This form, other than being more precise, it's also faster because nix-env does not have to parse all the derivations.
- For completeness: you may install graphvizCore with -A, since without the -A switch it's ambiguous.
+ For completeness: you must install graphvizCore with -A, since without the -A switch it's ambiguous.
In summary, it may happen when playing with nix that nix-env peeks a different derivation than nix-build. In such case you probably specified NIX_PATH, but nix-env is instead looking into ~/.nix-defexpr.