diff --git a/README.md b/README.md
index c0b6d4b1..1b35207b 100644
--- a/README.md
+++ b/README.md
@@ -513,7 +513,7 @@ There's several steps to getting this working:
 
 **1. Gunicorn deployment**:
 
-The `prometheus_multiproc_dir` environment variable must be set to a directory
+The `PROMETHEUS_MULTIPROC_DIR` environment variable must be set to a directory
 that the client library can use for metrics. This directory must be wiped
 between Gunicorn runs (before startup is recommended).