diff --git a/scheduler-server/src/main/java/gov/nasa/jpl/aerie/scheduler/server/services/GraphQLMerlinService.java b/scheduler-server/src/main/java/gov/nasa/jpl/aerie/scheduler/server/services/GraphQLMerlinService.java
index 4ff2cce735..7ce038691e 100644
--- a/scheduler-server/src/main/java/gov/nasa/jpl/aerie/scheduler/server/services/GraphQLMerlinService.java
+++ b/scheduler-server/src/main/java/gov/nasa/jpl/aerie/scheduler/server/services/GraphQLMerlinService.java
@@ -465,6 +465,7 @@ public void updatePlanActivityDirectiveAnchors(final PlanId planId, final List<S
   throws MerlinServiceException, IOException
   {
     final var request = new StringBuilder();
+    if (acts.isEmpty()) return;
     request.append("mutation {");
     for (SchedulingActivityDirective act: acts) {
       final var id = instancesToIds.get(act).id();