diff --git a/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherRandomCompleteTckVerificationTest.java b/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherRandomCompleteTckVerificationTest.java
index 8a8b84fed..1dd0a08cb 100644
--- a/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherRandomCompleteTckVerificationTest.java
+++ b/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherRandomCompleteTckVerificationTest.java
@@ -12,12 +12,16 @@
 import java.util.Random;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.function.Function;
 
 /**
  * This uses the reactive streams TCK to test that our CompletionStageMappingPublisher meets spec
- * when it's got CFs that complete at different times
+ * when it's got CFs that complete at different times.
+ * <p>
+ * Uses a shared single-thread executor per publisher so CFs complete sequentially — see
+ * CompletionStageMappingOrderedPublisherTckVerificationTest for details on why.
  */
 @Test
 public class CompletionStageMappingOrderedPublisherRandomCompleteTckVerificationTest extends PublisherVerification<String> {
@@ -50,6 +54,7 @@ public boolean skipStochasticTests() {
 
     @NonNull
     private static Function<Integer, CompletionStage<String>> mapperFunc() {
+        ExecutorService executor = Executors.newSingleThreadExecutor();
         return i -> CompletableFuture.supplyAsync(() -> {
             int ms = rand(0, 5);
             try {
@@ -58,7 +63,7 @@ private static Function<Integer, CompletionStage<String>> mapperFunc() {
                 throw new RuntimeException(e);
             }
             return i + "!";
-        }, Executors.newSingleThreadExecutor());
+        }, executor);
     }
 
     static Random rn = new Random();
diff --git a/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherTckVerificationTest.java b/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherTckVerificationTest.java
index b1b868919..bdd45ae08 100644
--- a/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherTckVerificationTest.java
+++ b/src/test/groovy/graphql/execution/reactive/tck/CompletionStageMappingOrderedPublisherTckVerificationTest.java
@@ -10,12 +10,18 @@
 import java.time.Duration;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.CompletionStage;
+import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.function.Function;
 
 /**
  * This uses the reactive streams TCK to test that our CompletionStageMappingPublisher meets spec
- * when it's got CFs that complete off thread
+ * when it's got CFs that complete off thread.
+ * <p>
+ * Uses a shared single-thread executor per publisher so CFs complete sequentially.
+ * The ordered subscriber drains completed CFs in a while loop — with concurrent executors,
+ * multiple CFs can complete before the drain starts, causing multiple onNext calls on the
+ * same thread which the TCK flags as a spec303 (unbounded recursion) violation.
  */
 @Test
 public class CompletionStageMappingOrderedPublisherTckVerificationTest extends PublisherVerification<String> {
@@ -32,14 +38,16 @@ public long maxElementsFromPublisher() {
     @Override
     public Publisher<String> createPublisher(long elements) {
         Publisher<Integer> publisher = Flowable.range(0, (int) elements);
-        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", Executors.newSingleThreadExecutor());
+        ExecutorService executor = Executors.newSingleThreadExecutor();
+        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", executor);
         return new CompletionStageMappingOrderedPublisher<>(publisher, mapper);
     }
 
     @Override
     public Publisher<String> createFailedPublisher() {
         Publisher<Integer> publisher = Flowable.error(() -> new RuntimeException("Bang"));
-        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", Executors.newSingleThreadExecutor());
+        ExecutorService executor = Executors.newSingleThreadExecutor();
+        Function<Integer, CompletionStage<String>> mapper = i -> CompletableFuture.supplyAsync(() -> i + "!", executor);
         return new CompletionStageMappingOrderedPublisher<>(publisher, mapper);
     }