diff --git a/README.md b/README.md
index 351f707..28a0cb6 100644
--- a/README.md
+++ b/README.md
@@ -5,9 +5,12 @@ Tools for working with Certificate Transparency log tiles.
 ## Install
 
 ```bash
-go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctfetch@latest
+GOPRIVATE=git.ipng.ch go install git.ipng.ch/certificate-transparency/ctfetch/cmd/ctfetch@latest
 ```
 
+The GOPRIVATE environment variable skips _Go checksum database_ and _Go module proxy_ as these do
+not index modules on `git.ipng.ch`.
+
 ## Usage
 
 `ctfetch` operates in two modes depending on the arguments given.