diff --git a/README b/README
index fa7cbfe..de94178 100644
--- a/README
+++ b/README
@@ -29,6 +29,7 @@ variables:
 * COMPILER_VERSION
 * MPI
 * MPI_VERSION
+* PLATFORM
 * HOSTNAME
 
 Sit detects currently the build platform using the HOSTNAME variable. If sit