diff --git a/man1/du.1 b/man1/du.1
index 73682b218..152b153a0 100644
--- a/man1/du.1
+++ b/man1/du.1
@@ -169,9 +169,10 @@ affects the HP-UX
 .B du
 program.
 .SH ENVIRONMENT
-The variable POSIXLY_CORRECT determines the choice of unit.
-If it is not set, and the variable BLOCKSIZE has a value starting
-with `HUMAN', then behaviour is as for the \-h option,
+The POSIXLY_CORRECT environment variable determines the choice of unit.
+If it is not set, 
+and the BLOCKSIZE environment variable has a value starting
+with `human', then behaviour is as for the \-h option,
 unless overridden by \-k or \-m options.
 The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have the
 usual meaning.