diff --git a/engine/table/src/main/java/io/deephaven/engine/table/impl/QueryTable.java b/engine/table/src/main/java/io/deephaven/engine/table/impl/QueryTable.java
index bbb385374a6..5419f0ced8e 100644
--- a/engine/table/src/main/java/io/deephaven/engine/table/impl/QueryTable.java
+++ b/engine/table/src/main/java/io/deephaven/engine/table/impl/QueryTable.java
@@ -757,6 +757,7 @@ public Table aggAllBy(AggSpec spec, ColumnName... groupByColumns) {
      * @param tableColumns the table columns
      * @return the aggregation, if non-empty
      */
+    @VisibleForTesting
     static Optional<Aggregation> singleAggregation(
             AggSpec spec, Collection<? extends ColumnName> groupByColumns,
             Collection<? extends ColumnName> tableColumns) {
diff --git a/extensions/parquet/base/src/main/java/io/deephaven/parquet/base/LevelsController.java b/extensions/parquet/base/src/main/java/io/deephaven/parquet/base/LevelsController.java
index 07faeb3a96f..b6e1cd89799 100644
--- a/extensions/parquet/base/src/main/java/io/deephaven/parquet/base/LevelsController.java
+++ b/extensions/parquet/base/src/main/java/io/deephaven/parquet/base/LevelsController.java
@@ -162,6 +162,11 @@ public void addElements(int elementsCount) {
 
         @Override
         public void addValues(int valuesCount) {
+            if (rangeCap.position() == 0) {
+                throw new IllegalStateException("Cannot add more values to this repeating level. It's possible that a "
+                        + "single row is getting split across pages, which is not supported.");
+                // TODO(deephaven-core:#4628) - Support this case
+            }
             rangeCap.put(rangeCap.position() - 1, childValueCount += valuesCount);
         }