diff --git a/src/main/java/org/disq_bio/disq/serializer/DisqKryoRegistrator.java b/src/main/java/org/disq_bio/disq/serializer/DisqKryoRegistrator.java
index fdfd3b5..ebd6de1 100644
--- a/src/main/java/org/disq_bio/disq/serializer/DisqKryoRegistrator.java
+++ b/src/main/java/org/disq_bio/disq/serializer/DisqKryoRegistrator.java
@@ -28,8 +28,10 @@
 import static com.google.common.base.Preconditions.checkNotNull;
 
 import com.esotericsoftware.kryo.Kryo;
+import com.esotericsoftware.kryo.serializers.JavaSerializer;
 import de.javakaffee.kryoserializers.CollectionsEmptyListSerializer;
 import de.javakaffee.kryoserializers.CollectionsSingletonListSerializer;
+import de.javakaffee.kryoserializers.UnmodifiableCollectionsSerializer;
 import org.apache.spark.serializer.KryoRegistrator;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -46,6 +48,7 @@ public void registerClasses(final Kryo kryo) {
 
     // htsjdk.samtools
     kryo.register(htsjdk.samtools.AlignmentBlock.class);
+    kryo.register(htsjdk.samtools.BAMRecord.class);
     kryo.register(htsjdk.samtools.Chunk.class);
     kryo.register(htsjdk.samtools.Cigar.class);
     kryo.register(htsjdk.samtools.CigarElement.class);
@@ -79,7 +82,8 @@ public void registerClasses(final Kryo kryo) {
     kryo.register(htsjdk.variant.variantcontext.CommonInfo.class);
     kryo.register(htsjdk.variant.variantcontext.FastGenotype.class);
     kryo.register(htsjdk.variant.variantcontext.GenotypeType.class);
-    kryo.register(htsjdk.variant.variantcontext.LazyGenotypesContext.class);
+    // Use JavaSerializer for LazyGenotypesContext to handle transient fields correctly
+    kryo.register(htsjdk.variant.variantcontext.LazyGenotypesContext.class, new JavaSerializer());
     kryo.register(htsjdk.variant.variantcontext.VariantContext.class);
     kryo.register(htsjdk.variant.variantcontext.VariantContext.Type.class);
 
@@ -116,6 +120,8 @@ public void registerClasses(final Kryo kryo) {
     kryo.register(java.util.LinkedHashSet.class);
     kryo.register(java.util.TreeSet.class);
 
+    UnmodifiableCollectionsSerializer.registerSerializers(kryo);
+
     // org.apache.spark.internal.io
     kryo.register(org.apache.spark.internal.io.FileCommitProtocol.TaskCommitMessage.class);
 
diff --git a/src/test/java/org/disq_bio/disq/HtsjdkReadsRddTest.java b/src/test/java/org/disq_bio/disq/HtsjdkReadsRddTest.java
index 9c15fc0..f518e6e 100644
--- a/src/test/java/org/disq_bio/disq/HtsjdkReadsRddTest.java
+++ b/src/test/java/org/disq_bio/disq/HtsjdkReadsRddTest.java
@@ -108,6 +108,9 @@ public void testReadAndWrite(
 
     HtsjdkReadsRdd htsjdkReadsRdd = htsjdkReadsRddStorage.read(inputPath);
 
+    // reduce to realize the RDD of reads
+    Assert.assertNotNull(htsjdkReadsRdd.getReads().first());
+
     // read the file using htsjdk to get expected number of reads, then count the number in the RDD
     int expectedCount = AnySamTestUtil.countReads(inputPath, refPath);
     Assert.assertEquals(expectedCount, htsjdkReadsRdd.getReads().count());
diff --git a/src/test/java/org/disq_bio/disq/HtsjdkVariantsRddTest.java b/src/test/java/org/disq_bio/disq/HtsjdkVariantsRddTest.java
index 61dc871..3ef0e0c 100644
--- a/src/test/java/org/disq_bio/disq/HtsjdkVariantsRddTest.java
+++ b/src/test/java/org/disq_bio/disq/HtsjdkVariantsRddTest.java
@@ -71,6 +71,9 @@ public void testReadAndWrite(
 
     HtsjdkVariantsRdd htsjdkVariantsRdd = htsjdkVariantsRddStorage.read(inputPath);
 
+    // reduce to realize the RDD of variants
+    Assert.assertNotNull(htsjdkVariantsRdd.getVariants().first());
+
     // read the file using htsjdk to get expected number of reads, then count the number in the RDD
     int expectedCount = countVariants(inputPath);
     Assert.assertEquals(expectedCount, htsjdkVariantsRdd.getVariants().count());