diff --git a/man7/environ.7 b/man7/environ.7
index 47761a950..f683b6028 100644
--- a/man7/environ.7
+++ b/man7/environ.7
@@ -52,9 +52,15 @@ it inherits a
 .I copy
 of its parent's environment.
 .PP
-By convention the strings in
+By convention, the strings in
 .I environ
 have the form "\fIname\fP\fB=\fP\fIvalue\fP".
+Names of environment variables are case-sensitive and must not contain
+the character "\fB=\fP". The values of environment variables can be anything
+that can be represented as a string. A value and a name must not contain an
+embedded null byte (\(aq\e0\(aq),
+since this is assumed to terminate the string.
+.PP
 Common examples are:
 .TP
 .B USER