diff --git a/contrib/prometheus-exporter/README b/contrib/prometheus-exporter/README
index fdbc502..e41ebdc 100644
--- a/contrib/prometheus-exporter/README
+++ b/contrib/prometheus-exporter/README
@@ -12,9 +12,10 @@
 
 However, PROMEX is not built by default with HAProxy. It is provided as an extra
 component for everyone want to use it. So you need to explicitly build HAProxy
-with the PROMEX service, using the Makefile variable "EXTRA_OBJS". For instance:
+with the PROMEX service, setting the Makefile variable "USE_PROMEX" to "1". For
+instance:
 
-    > make TARGET=linux-glibc EXTRA_OBJS="contrib/prometheus-exporter/service-prometheus.o"
+    > make TARGET=linux-glibc USE_PROMEX=1
 
 if HAProxy provides the PROMEX service, the following build option will be
 reported by the command "haproxy -vv":