diff --git a/java/core/src/main/java/com/google/protobuf/ProtobufToStringOutput.java b/java/core/src/main/java/com/google/protobuf/ProtobufToStringOutput.java
index e6df9267d7884..f3deb3e8e64e1 100644
--- a/java/core/src/main/java/com/google/protobuf/ProtobufToStringOutput.java
+++ b/java/core/src/main/java/com/google/protobuf/ProtobufToStringOutput.java
@@ -1,10 +1,12 @@
 package com.google.protobuf;
 
+import java.util.Optional;
+
 /**
- * ProtobufToStringOutput controls the output format of {@link Message#toString()}. Specifically, for
- * the Runnable object passed to `callWithDebugFormat` and `callWithTextFormat`, Message.toString()
- * will always output the specified format unless ProtobufToStringOutput is used again to change the
- * output format.
+ * ProtobufToStringOutput controls the output format of {@link Message#toString()}. Specifically,
+ * for the Runnable object passed to `callWithDebugFormat` and `callWithTextFormat`,
+ * Message.toString() will always output the specified format unless ProtobufToStringOutput is used
+ * again to change the output format.
  */
 public final class ProtobufToStringOutput {
   private enum OutputMode {
@@ -13,12 +15,14 @@ private enum OutputMode {
   }
 
   private static final ThreadLocal<OutputMode> outputMode =
-      new ThreadLocal<OutputMode>() {
-        @Override
-        protected OutputMode initialValue() {
-          return OutputMode.TEXT_FORMAT;
-        }
-      };
+      ThreadLocal.withInitial(() -> OutputMode.TEXT_FORMAT);
+
+  // Many tests are bound to the traditional Message.toString() output format (the text format). To
+  // accelerate the debug format adoption while avoiding breaking such tests, we introduce this
+  // test-only flag to disable the debug format in tests for certain libraries in which the output
+  // of Message.toString() is unlikely to be deserialized.
+  private static final ThreadLocal<Boolean> disableDebugFormatForTests =
+      ThreadLocal.withInitial(() -> false);
 
   private ProtobufToStringOutput() {}
 
@@ -49,4 +53,8 @@ public static void callWithTextFormat(Runnable impl) {
   public static boolean shouldOutputDebugFormat() {
     return outputMode.get() == OutputMode.DEBUG_FORMAT;
   }
+
+  static void setDisableDebugFormatForTests(boolean disable) {
+    disableDebugFormatForTests.set(disable);
+  }
 }