diff --git a/src/Reassem.cc b/src/Reassem.cc
index 333452433a..898276d0e4 100644
--- a/src/Reassem.cc
+++ b/src/Reassem.cc
@@ -24,9 +24,17 @@ void DataBlockList::DataSize(uint64_t seq_cutoff, uint64_t* below, uint64_t* abo
 		const auto& b = e.second;
 
 		if ( b.seq <= seq_cutoff )
-			*above += b.Size();
+			{
+			if ( b.upper <= seq_cutoff )
+				*below += b.Size();
+			else
+				{
+				*below += seq_cutoff - b.seq;
+				*above += b.upper - seq_cutoff;
+				}
+			}
 		else
-			*below += b.Size();
+			*above += b.Size();
 		}
 	}
 
diff --git a/src/Reassem.h b/src/Reassem.h
index 798c1bcca4..5c056bfd74 100644
--- a/src/Reassem.h
+++ b/src/Reassem.h
@@ -155,12 +155,13 @@ public:
 		{ return total_data_size; }
 
 	/**
-	 * Counts the total size of all list elements paritioned by some cuttof.
+	 * Counts the total size of all data contained in list elements
+	 * partitioned by some cutoff.
 	 * WARNING: this is an O(n) operation and potentially very slow.
 	 * @param seq_cutoff  the sequence number used to partition
 	 * element sizes returned via "below" and "above" parameters
-	 * @param below  the size in bytes of all elements below "seq_cutoff"
-	 * @param above  the size in bytes of all elements above "seq_cutoff"
+	 * @param below  the size in bytes of all data below "seq_cutoff"
+	 * @param above  the size in bytes of all data above "seq_cutoff"
 	 */
 	void DataSize(uint64_t seq_cutoff, uint64_t* below, uint64_t* above) const;