diff --git a/metropolis/node/core/curator/impl_leader_management.go b/metropolis/node/core/curator/impl_leader_management.go
index bc65e42..fd593c3 100644
--- a/metropolis/node/core/curator/impl_leader_management.go
+++ b/metropolis/node/core/curator/impl_leader_management.go
@@ -218,9 +218,7 @@
 			// TODO(mateusz@monogon.tech): update the API to use protobuf Duration
 			// message, in order to facilitate filter expressions like
 			// 'node.HeartbeatTimestamp > duration("30s")'.
-			// TODO(mateusz@monogon.tech): change HeartbeatTimestamp proto field
-			// name to TimeSinceHeartbeat, since it's not really a timestamp.
-			HeartbeatTimestamp: lhb.Nanoseconds(),
+			TimeSinceHeartbeat: lhb.Nanoseconds(),
 			Health:             health,
 		}
 
diff --git a/metropolis/proto/api/management.proto b/metropolis/proto/api/management.proto
index ba20cee..b48e2b1 100644
--- a/metropolis/proto/api/management.proto
+++ b/metropolis/proto/api/management.proto
@@ -137,10 +137,10 @@
       HEARTBEAT_TIMEOUT = 3;
     }
     Health health = 5;
-    // heartbeat_timestamp is the duration since the last of the node's
-    // heartbeats was received, expressed in nanoseconds. It equals zero if no
-    // heartbeats were received.
-    int64 heartbeat_timestamp = 6;
+    // time_since_heartbeat is the duration since the last of the node's
+    // heartbeats was received, expressed in nanoseconds. It is only valid with
+    // the health status of either HEALTHY or HEARTBEAT_TIMEOUT.
+    int64 time_since_heartbeat = 6;
 }
 
 message ApproveNodeRequest {