diff --git a/ipam/allocator.go b/ipam/allocator.go
index 478c6545..f3388a67 100644
--- a/ipam/allocator.go
+++ b/ipam/allocator.go
@@ -321,11 +321,11 @@ func (alloc *Allocator) ContainerStarted(ident string) {
 }
 
 func (alloc *Allocator) PruneOwned(ids []string) {
+	idmap := make(map[string]struct{}, len(ids))
+	for _, id := range ids {
+		idmap[id] = struct{}{}
+	}
 	alloc.actionChan <- func() {
-		idmap := make(map[string]struct{}, len(ids))
-		for _, id := range ids {
-			idmap[id] = struct{}{}
-		}
 		alloc.pruneOwned(idmap)
 	}
 }