diff --git a/policy/diamond/policy/tiled/tiled.rego b/policy/diamond/policy/tiled/tiled.rego
index f3c7cd8..17644b2 100644
--- a/policy/diamond/policy/tiled/tiled.rego
+++ b/policy/diamond/policy/tiled/tiled.rego
@@ -27,13 +27,13 @@ _session := data.diamond.data.proposals[format_int(input.proposal, 10)].sessions
 
 # Returns the session ID if the subject has write permissions for the
 # specific beamline, visit and proposal requested in the input.
-user_session := to_number(_session) if {
+user_session := format_int(_session, 10) if {
 	session.write_to_beamline_visit
 	_session
 }
 
 # service account check
-user_session := to_number(_session) if {
+user_session := format_int(_session, 10) if {
 	input.beamline == token.claims.beamline
 	input.beamline == session.beamline_for(input.proposal, input.visit)
 	_session in data.diamond.data.beamlines[input.beamline].sessions
@@ -81,20 +81,20 @@ user_sessions contains "*" if {
 	admin.is_admin(token.claims.fedid)
 }
 
-user_sessions contains to_number(session) if {
+user_sessions contains format_int(session, 10) if {
 	subject
 	not admin.is_admin(token.claims.fedid)
 	some session in subject.sessions
 }
 
-user_sessions contains to_number(session) if {
+user_sessions contains format_int(session, 10) if {
 	subject
 	not admin.is_admin(token.claims.fedid)
 	some beamline in beamlines
 	some session in data.diamond.data.beamlines[beamline].sessions
 }
 
-user_sessions contains to_number(session) if {
+user_sessions contains format_int(session, 10) if {
 	subject
 	not admin.is_admin(token.claims.fedid)
 	some p in subject.proposals
@@ -103,7 +103,7 @@ user_sessions contains to_number(session) if {
 }
 
 # service account check
-user_sessions contains to_number(session) if {
+user_sessions contains format_int(session, 10) if {
 	not subject
 	some session in data.diamond.data.beamlines[token.claims.beamline].sessions
 }
diff --git a/policy/diamond/policy/tiled/tiled_test.rego b/policy/diamond/policy/tiled/tiled_test.rego
index 3407d9c..8d8cd30 100644
--- a/policy/diamond/policy/tiled/tiled_test.rego
+++ b/policy/diamond/policy/tiled/tiled_test.rego
@@ -93,20 +93,20 @@ diamond_data := {
 test_user_session_tags if {
 	tiled.user_sessions == set() with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "oscar"}
-	tiled.user_sessions == {11, 12} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"11", "12"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "alice"}
-	tiled.user_sessions == {11, 12, 13, 14} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"11", "12", "13", "14"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "bob"}
 	tiled.user_sessions == {"*"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "carol"}
-	tiled.user_sessions == {13, 14} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"13", "14"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "desmond"}
-	tiled.user_sessions == {13, 14} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"13", "14"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"fedid": "edna"}
 }
 
 test_user_session_allow if {
-	tiled.user_session == 11 with data.diamond.data as diamond_data
+	tiled.user_session == "11" with data.diamond.data as diamond_data
 		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
 		with data.diamond.policy.token.claims as {"fedid": "carol"}
 }
@@ -132,7 +132,7 @@ test_modify_session if {
 # Service account tests
 
 test_user_session_allow_service_account_on_beamline if {
-	tiled.user_session == 11 with data.diamond.data as diamond_data
+	tiled.user_session == "11" with data.diamond.data as diamond_data
 		with input as {"beamline": "i03", "proposal": 1, "visit": 1}
 		with data.diamond.policy.token.claims as {"beamline": "i03"}
 }
@@ -168,9 +168,9 @@ test_modify_session_on_none_existent_beamline if {
 }
 
 test_user_session_tags_service_account if {
-	tiled.user_sessions == {11} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"11"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"beamline": "i03"}
-	tiled.user_sessions == {12, 13, 14} with data.diamond.data as diamond_data
+	tiled.user_sessions == {"12", "13", "14"} with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"beamline": "b07"}
 	tiled.user_sessions == set() with data.diamond.data as diamond_data
 		with data.diamond.policy.token.claims as {"beamline": "b007"}