diff --git a/sled-agent/src/common/instance.rs b/sled-agent/src/common/instance.rs
index 43ffa29c41..ed0aceff82 100644
--- a/sled-agent/src/common/instance.rs
+++ b/sled-agent/src/common/instance.rs
@@ -114,7 +114,7 @@ impl ObservedPropolisState {
     /// runtime state and an instance state monitor response received from
     /// Propolis.
     pub fn new(
-        migration: Option<&MigrationRuntimeState>,
+        instance_runtime: &InstanceRuntimeState,
         propolis_state: &InstanceStateMonitorResponse,
     ) -> Self {
         // If there's no migration currently registered with this sled, report
@@ -122,7 +122,14 @@ impl ObservedPropolisState {
         // even if Propolis has some migration data to share. (This case arises
         // when Propolis returns state from a previous migration that sled agent
         // has already retired.)
-        let Some(migration) = migration else {
+        //
+        // N.B. This needs to be read from the instance runtime state and not
+        //      the migration runtime state to ensure that, once a migration in
+        //      completes, the "completed" observation is reported to
+        //      `InstanceStates::apply_propolis_observation` exactly once.
+        //      Otherwise that routine will try to apply the "inbound migration
+        //      complete" instance state transition twice.
+        let Some(migration_id) = instance_runtime.migration_id else {
             return Self {
                 vmm_state: PropolisInstanceState(propolis_state.state),
                 migration_status: ObservedMigrationStatus::NoMigration,
@@ -136,12 +143,8 @@ impl ObservedPropolisState {
             &propolis_state.migration.migration_in,
             &propolis_state.migration.migration_out,
         ) {
-            (Some(inbound), _) if inbound.id == migration.migration_id => {
-                inbound
-            }
-            (_, Some(outbound)) if outbound.id == migration.migration_id => {
-                outbound
-            }
+            (Some(inbound), _) if inbound.id == migration_id => inbound,
+            (_, Some(outbound)) if outbound.id == migration_id => outbound,
             _ => {
                 // Sled agent believes this instance should be migrating, but
                 // Propolis isn't reporting a matching migration yet, so assume
diff --git a/sled-agent/src/instance.rs b/sled-agent/src/instance.rs
index 1f80b736b4..04b68ef752 100644
--- a/sled-agent/src/instance.rs
+++ b/sled-agent/src/instance.rs
@@ -373,7 +373,7 @@ impl InstanceRunner {
                     match request {
                         Some(Update { state, tx }) => {
                             let observed = ObservedPropolisState::new(
-                                self.state.migration(),
+                                self.state.instance(),
                                 &state,
                             );
                             let reaction = self.observe_state(&observed).await;
diff --git a/sled-agent/src/sim/instance.rs b/sled-agent/src/sim/instance.rs
index 762490bd6c..06739df8fa 100644
--- a/sled-agent/src/sim/instance.rs
+++ b/sled-agent/src/sim/instance.rs
@@ -278,7 +278,7 @@ impl SimInstanceInner {
             }
 
             self.state.apply_propolis_observation(&ObservedPropolisState::new(
-                self.state.migration(),
+                self.state.instance(),
                 &self.last_response,
             ))
         } else {