1 files changed, 6 insertions, 1 deletions
diff --git a/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java b/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
index b577495d..b192b53e 100644
--- a/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
+++ b/java/util/src/main/java/com/google/protobuf/util/FieldMaskTree.java
@@ -217,7 +217,12 @@ final class FieldMaskTree {
       Message source,
       Message.Builder destination,
       FieldMaskUtil.MergeOptions options) {
-    assert source.getDescriptorForType() == destination.getDescriptorForType();
+    if (source.getDescriptorForType() != destination.getDescriptorForType()) {
+      throw new IllegalArgumentException(
+          String.format(
+              "source (%s) and destination (%s) descriptor must be equal",
+              source.getDescriptorForType(), destination.getDescriptorForType()));
+    }
 
     Descriptor descriptor = source.getDescriptorForType();
     for (Entry<String, Node> entry : node.children.entrySet()) {