diff --git a/policies/authorization_grant/authorization_grant.rego b/policies/authorization_grant/authorization_grant.rego
index 72fa7ee8b..e999ebb70 100644
--- a/policies/authorization_grant/authorization_grant.rego
+++ b/policies/authorization_grant/authorization_grant.rego
@@ -67,11 +67,32 @@ allowed_scope(scope) if {
 	regex.match(`^urn:matrix:org.matrix.msc2967.client:device:[A-Za-z0-9._~!$&'()*+,;=:@/-]{10,}$`, scope)
 }
 
+allowed_scope(scope) if {
+	# Grant access to the C-S API only if there is a user
+	interactive_grant_type(input.grant_type)
+	regex.match(`^urn:matrix:client:device:[A-Za-z0-9._~!$&'()*+,;=:@/-]{10,}$`, scope)
+}
+
+allowed_scope("urn:matrix:client:api:*") if {
+	# Grant access to the C-S API only if there is a user
+	interactive_grant_type(input.grant_type)
+}
+
 allowed_scope("urn:matrix:org.matrix.msc2967.client:api:*") if {
 	# Grant access to the C-S API only if there is a user
 	interactive_grant_type(input.grant_type)
 }
 
+uses_unstable_scopes if {
+	scope_list := split(input.scope, " ")
+	count({scope | some scope in scope_list; startswith(scope, "urn:matrix:org.matrix.msc2967.client:")}) > 0
+}
+
+uses_stable_scopes if {
+	scope_list := split(input.scope, " ")
+	count({scope | some scope in scope_list; startswith(scope, "urn:matrix:client:")}) > 0
+}
+
 # METADATA
 # entrypoint: true
 violation contains {"msg": msg} if {
@@ -85,6 +106,16 @@ violation contains {"msg": "only one device scope is allowed at a time"} if {
 	count({scope | some scope in scope_list; startswith(scope, "urn:matrix:org.matrix.msc2967.client:device:")}) > 1
 }
 
+violation contains {"msg": "only one device scope is allowed at a time"} if {
+	scope_list := split(input.scope, " ")
+	count({scope | some scope in scope_list; startswith(scope, "urn:matrix:client:device:")}) > 1
+}
+
+violation contains {"msg": "request cannot mix unstable and stable scopes"} if {
+	uses_stable_scopes
+	uses_unstable_scopes
+}
+
 violation contains {"msg": sprintf(
 	"Requester [%s] isn't allowed to do this action",
 	[common.format_requester(input.requester)],
diff --git a/policies/authorization_grant/authorization_grant_test.rego b/policies/authorization_grant/authorization_grant_test.rego
index 3594bfac2..fdf097da2 100644
--- a/policies/authorization_grant/authorization_grant_test.rego
+++ b/policies/authorization_grant/authorization_grant_test.rego
@@ -35,7 +35,7 @@ test_standard_scopes if {
 		with input.scope as "profile"
 }
 
-test_matrix_scopes if {
+test_matrix_unstable_scopes if {
 	authorization_grant.allow with input.user as user
 		with input.client as client
 		with input.grant_type as "authorization_code"
@@ -52,7 +52,24 @@ test_matrix_scopes if {
 		with input.scope as "urn:matrix:org.matrix.msc2967.client:api:*"
 }
 
-test_device_scopes if {
+test_matrix_stable_scopes if {
+	authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:api:*"
+
+	authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "urn:ietf:params:oauth:grant-type:device_code"
+		with input.scope as "urn:matrix:client:api:*"
+
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "client_credentials"
+		with input.scope as "urn:matrix:client:api:*"
+}
+
+test_unstable_device_scopes if {
 	authorization_grant.allow with input.user as user
 		with input.client as client
 		with input.grant_type as "authorization_code"
@@ -87,6 +104,58 @@ test_device_scopes if {
 		with input.scope as "urn:matrix:org.matrix.msc2967.client:device:AAbbCCdd01"
 }
 
+test_stable_device_scopes if {
+	authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:device:AAbbCCdd01"
+
+	authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:device:AAbbCCdd01-asdasdsa1-2313"
+
+	# Too short
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:device:abcd"
+
+	# Multiple device scope
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:device:AAbbCCdd01 urn:matrix:client:device:AAbbCCdd02"
+
+	# Allowed with the device code grant
+	authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "urn:ietf:params:oauth:grant-type:device_code"
+		with input.scope as "urn:matrix:client:device:AAbbCCdd01"
+
+	# Not authorization_grant.allowed for the client credentials grant
+	not authorization_grant.allow with input.client as client
+		with input.grant_type as "client_credentials"
+		with input.scope as "urn:matrix:client:device:AAbbCCdd01"
+}
+
+test_mix_stable_and_unstable_scopes if {
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:org.matrix.msc2967.client:api:* urn:matrix:client:device:AAbbCCdd01"
+
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:api:* urn:matrix:org.matrix.msc2967.client:device:AAbbCCdd01"
+
+	not authorization_grant.allow with input.user as user
+		with input.client as client
+		with input.grant_type as "authorization_code"
+		with input.scope as "urn:matrix:client:api:* urn:matrix:org.matrix.msc2967.client:api:*"
+}
+
 test_synapse_admin_scopes if {
 	some grant_type in ["authorization_code", "urn:ietf:params:oauth:grant-type:device_code"]