diff --git a/principles/fp-000-summary.md b/principles/fp-000-summary.md
index b2a4966e9..9edd13a57 100644
--- a/principles/fp-000-summary.md
+++ b/principles/fp-000-summary.md
@@ -34,7 +34,7 @@ P10) <b>Commitment To Collaboration</b> - OBO Foundry ontology development, in c
 
 P11) <b>Locus of Authority</b> - There should be a person who is responsible for communications between the community and the ontology developers, for communicating with the Foundry on all Foundry-related matters, for mediating discussions involving maintenance in the light of scientific advance, and for ensuring that all user feedback is addressed.
 
-P12) <b>Naming Conventions</b> - The names (primary labels) for elements (classes, properties, etc.) in an ontology must be intelligible to scientists and amenable to natural language processing. Primary labels should be unique among OBO Library ontologies.
+P12) <b>Naming Conventions</b> - The names (primary labels) for elements (classes, properties, etc.) in an ontology must be intelligible to scientists and amenable to natural language processing. Each primary label SHOULD be unique among OBO Library ontologies, and MUST be unique within its own ontology.
 
 P13) <b>Notification of Changes</b> - Ontologies SHOULD announce major changes to relevant stakeholders and collaborators ahead of release.