diff --git a/scio-smb/src/main/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransform.java b/scio-smb/src/main/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransform.java
index 44c44455c3..b4b0a2457e 100644
--- a/scio-smb/src/main/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransform.java
+++ b/scio-smb/src/main/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransform.java
@@ -53,12 +53,14 @@
 import org.apache.beam.sdk.transforms.Filter;
 import org.apache.beam.sdk.transforms.PTransform;
 import org.apache.beam.sdk.transforms.ParDo;
+import org.apache.beam.sdk.transforms.Reshuffle;
 import org.apache.beam.sdk.transforms.display.DisplayData;
 import org.apache.beam.sdk.transforms.join.CoGbkResult;
 import org.apache.beam.sdk.transforms.join.CoGbkResultSchema;
 import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
 import org.apache.beam.sdk.values.KV;
 import org.apache.beam.sdk.values.PBegin;
+import org.apache.beam.sdk.values.PCollection;
 import org.apache.beam.sdk.values.PCollectionView;
 import org.apache.beam.sdk.values.TupleTag;
 import org.apache.beam.sdk.values.TupleTagList;
@@ -83,6 +85,7 @@ public class SortedBucketTransform<FinalKeyT, FinalValueT> extends PTransform<PB
   private final BucketSource<FinalKeyT> bucketSource;
   private final DoFn<Iterable<MergedBucket>, KV<BucketShardId, ResourceId>> finalizeBuckets;
   private final ParDo.SingleOutput<BucketItem, MergedBucket> doFn;
+  private final boolean usesSideInputs;
 
   public SortedBucketTransform(
       List<SortedBucketSource.BucketedInput<?>> sources,
@@ -99,13 +102,14 @@ public SortedBucketTransform(
       String filenameSuffix,
       String filenamePrefix) {
     Preconditions.checkNotNull(outputDirectory, "outputDirectory is not set");
+    usesSideInputs = sideInputTransformFn != null;
     Preconditions.checkState(
-        !((transformFn == null) && (sideInputTransformFn == null)), // at least one defined
+        transformFn != null || usesSideInputs, // at least one defined
         "At least one of transformFn and sideInputTransformFn must be set");
     Preconditions.checkState(
-        !((transformFn != null) && (sideInputTransformFn != null)), // only one defined
+        transformFn == null || !usesSideInputs, // only one defined
         "At most one of transformFn and sideInputTransformFn may be set");
-    if (sideInputTransformFn != null) {
+    if (usesSideInputs) {
       Preconditions.checkNotNull(sides, "If using sideInputTransformFn, sides must not be null");
     }
 
@@ -151,11 +155,18 @@ public SortedBucketTransform(
 
   @Override
   public final WriteResult expand(final PBegin begin) {
-    return WriteResult.fromTuple(
+    PCollection<BucketItem> bucketOffsets =
         begin
             .getPipeline()
             // outputs bucket offsets for the various SMB readers
-            .apply("BucketOffsets", Read.from(bucketSource))
+            .apply("BucketOffsets", Read.from(bucketSource));
+
+    if (usesSideInputs) {
+      bucketOffsets = bucketOffsets.apply("RedistributeBuckets", Reshuffle.viaRandomKey());
+    }
+
+    return WriteResult.fromTuple(
+        bucketOffsets
             .apply("MergeBuckets", this.doFn)
             .apply(Filter.by(Objects::nonNull))
             .apply(Group.globally())
diff --git a/scio-smb/src/test/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransformTest.java b/scio-smb/src/test/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransformTest.java
index ad6f8c1c33..7dc5e3bab2 100644
--- a/scio-smb/src/test/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransformTest.java
+++ b/scio-smb/src/test/java/org/apache/beam/sdk/extensions/smb/SortedBucketTransformTest.java
@@ -26,11 +26,14 @@
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
 import java.util.stream.Collectors;
+import org.apache.beam.sdk.Pipeline;
+import org.apache.beam.sdk.Pipeline.PipelineVisitor.CompositeBehavior;
 import org.apache.beam.sdk.PipelineResult;
 import org.apache.beam.sdk.coders.StringUtf8Coder;
 import org.apache.beam.sdk.extensions.smb.SMBFilenamePolicy.FileAssignment;
@@ -41,6 +44,7 @@
 import org.apache.beam.sdk.io.fs.MatchResult.Status;
 import org.apache.beam.sdk.io.fs.ResourceId;
 import org.apache.beam.sdk.metrics.DistributionResult;
+import org.apache.beam.sdk.runners.TransformHierarchy;
 import org.apache.beam.sdk.testing.TestPipeline;
 import org.apache.beam.sdk.transforms.Create;
 import org.apache.beam.sdk.transforms.View;
@@ -101,6 +105,28 @@ public class SortedBucketTransformTest {
                           .getAll(new TupleTag<String>("rhs"))
                           .forEach(rhs -> outputConsumer.accept(lhs + "-" + rhs)));
 
+  private static Set<String> transformNames(Pipeline pipeline) {
+    Set<String> names = new HashSet<>();
+    pipeline.traverseTopologically(
+        new Pipeline.PipelineVisitor.Defaults() {
+          private void addName(TransformHierarchy.Node node) {
+            names.addAll(Arrays.asList(node.getFullName().split("/")));
+          }
+
+          @Override
+          public CompositeBehavior enterCompositeTransform(TransformHierarchy.Node node) {
+            addName(node);
+            return CompositeBehavior.ENTER_TRANSFORM;
+          }
+
+          @Override
+          public void visitPrimitiveTransform(TransformHierarchy.Node node) {
+            addName(node);
+          }
+        });
+    return names;
+  }
+
   private static List<BucketedInput<?>> makeSources(SortedBucketSource.Keying keying) {
     return ImmutableList.of(
         BucketedInput.of(
@@ -274,6 +300,7 @@ private void testWithSides(
             new TestFileOperations(),
             ".txt",
             SortedBucketIO.DEFAULT_FILENAME_PREFIX));
+    Assert.assertTrue(transformNames(transformPipeline).contains("RedistributeBuckets"));
     runAndValidate(targetParallelism, expectedNumBuckets, expectedWithSides);
   }
 
@@ -295,6 +322,7 @@ private void test(
             new TestFileOperations(),
             ".txt",
             SortedBucketIO.DEFAULT_FILENAME_PREFIX));
+    Assert.assertFalse(transformNames(transformPipeline).contains("RedistributeBuckets"));
     runAndValidate(targetParallelism, expectedNumBuckets, expected);
   }