diff --git a/internal/groups/events/events.go b/internal/groups/events/events.go
index d30b462c662..97dc52b01a7 100644
--- a/internal/groups/events/events.go
+++ b/internal/groups/events/events.go
@@ -39,7 +39,7 @@ var (
 
 type assignEvent struct {
 	operation string
-	memberID  []string
+	memberID  string
 	groupID   string
 	createdAt time.Time
 }
@@ -57,7 +57,7 @@ func (cge assignEvent) Encode() (map[string]interface{}, error) {
 
 type unassignEvent struct {
 	operation string
-	memberID  []string
+	memberID  string
 	groupID   string
 	createdAt time.Time
 }
diff --git a/internal/groups/events/streams.go b/internal/groups/events/streams.go
index 253574b7721..1834a6ce107 100644
--- a/internal/groups/events/streams.go
+++ b/internal/groups/events/streams.go
@@ -148,7 +148,7 @@ func (es eventStore) Assign(ctx context.Context, token, groupID, relation, membe
 	event := assignEvent{
 		operation: "group.assign",
 		groupID:   groupID,
-		memberID:  memberIDs,
+		memberID:  memberIDs[0],
 		createdAt: time.Now(),
 	}
 
@@ -167,7 +167,7 @@ func (es eventStore) Unassign(ctx context.Context, token, groupID, relation, mem
 	event := unassignEvent{
 		operation: "group.unassign",
 		groupID:   groupID,
-		memberID:  memberIDs,
+		memberID:  memberIDs[0],
 		createdAt: time.Now(),
 	}