diff --git a/core/trino-main/src/main/java/io/trino/operator/output/RleAwarePositionsAppender.java b/core/trino-main/src/main/java/io/trino/operator/output/RleAwarePositionsAppender.java
index 289608b9ad64..dbffe7983146 100644
--- a/core/trino-main/src/main/java/io/trino/operator/output/RleAwarePositionsAppender.java
+++ b/core/trino-main/src/main/java/io/trino/operator/output/RleAwarePositionsAppender.java
@@ -52,9 +52,9 @@ public RleAwarePositionsAppender(BlockPositionIsDistinctFrom isDistinctFromOpera
     @Override
     public void append(IntArrayList positions, Block source)
     {
-        // RleAwarePositionsAppender should be used with FlatteningPositionsAppender that makes sure
+        // RleAwarePositionsAppender should be used with UnnestingPositionsAppender that makes sure
         // append is called only with flat block
-        checkArgument(!(source instanceof RunLengthEncodedBlock));
+        checkArgument(!(source instanceof RunLengthEncodedBlock), "Append should be called with non-RLE block but got %s", source);
         switchToFlat();
         delegate.append(positions, source);
     }
diff --git a/core/trino-main/src/main/java/io/trino/operator/output/UnnestingPositionsAppender.java b/core/trino-main/src/main/java/io/trino/operator/output/UnnestingPositionsAppender.java
index c56f02b4c754..cedc3ece1cfd 100644
--- a/core/trino-main/src/main/java/io/trino/operator/output/UnnestingPositionsAppender.java
+++ b/core/trino-main/src/main/java/io/trino/operator/output/UnnestingPositionsAppender.java
@@ -117,6 +117,11 @@ public long getSizeInBytes()
     private void appendDictionary(IntArrayList positions, DictionaryBlock source)
     {
         Block dictionary = source.getDictionary();
+        if (dictionary instanceof RunLengthEncodedBlock rleDictionary) {
+            appendRle(rleDictionary.getValue(), positions.size());
+            return;
+        }
+
         IntArrayList dictionaryPositions = getDictionaryPositions(positions, source);
         if (dictionaryBlockBuilder.canAppend(dictionary)) {
             dictionaryBlockBuilder.append(dictionaryPositions, dictionary);