diff --git a/README.rst b/README.rst
index 171a178..8672031 100644
--- a/README.rst
+++ b/README.rst
@@ -100,7 +100,8 @@ not work inside of the group.
 
 Version constraints are a comma separated list of constraints where each
 constraint is  (== | < | <= | >= | > | !=) VERSION, and the constraints are ANDed
-together (the same as pip requirements version constraints).
+together (the same as pip requirements version constraints,
+except that they require a space between the dep and version constraints).
 
 Comments are allowed: everything from the first ``#`` to the end of the line is
 ignored.
@@ -170,6 +171,14 @@ This selects the ``ceph-common`` package when the profile ``ceph`` is
 specified. However, it will only select the ``python-rbd`` package when both
 ``ceph`` and ``glance`` profiles are active.
 
+To specify package versions::
+
+    python >=3.7,<=3.8
+    grep >=3.3
+
+    # OR with a platform profile
+    python [platform:brew] ==3.7.3
+
 For a more comprehensive example check bindep.txt_ file that is used to
 test bindep itself on multiple platforms.