diff --git a/changelogs/server_server/newsfragments/2191.clarification b/changelogs/server_server/newsfragments/2191.clarification
new file mode 100644
index 00000000..3247bbf5
--- /dev/null
+++ b/changelogs/server_server/newsfragments/2191.clarification
@@ -0,0 +1 @@
+Clarify what the `minimum_valid_until_ts` field means when it is set in key queries.
diff --git a/data/api/server-server/keys_query.yaml b/data/api/server-server/keys_query.yaml
index bc5df207..02d31568 100644
--- a/data/api/server-server/keys_query.yaml
+++ b/data/api/server-server/keys_query.yaml
@@ -37,7 +37,7 @@ paths:
             A millisecond POSIX timestamp. The returned keys SHOULD be valid
             until at least this timestamp.
 
-            If not supplied, the notary server SHOULD use the current time.
+            If not supplied, the notary server MUST use the current time.
           required: false
           example: 1234567890
           schema:
@@ -101,7 +101,7 @@ paths:
                             A millisecond POSIX timestamp. The returned keys
                             SHOULD be valid until at least this timestamp.
 
-                            If not supplied, the notary server SHOULD use the
+                            If not supplied, the notary server MUST use the
                             current time.
                           example: 1234567890
               required: