diff --git a/src/backend/access/common/detoast.c b/src/backend/access/common/detoast.c
index 2fef40c2e9..6c79bd2a40 100644
--- a/src/backend/access/common/detoast.c
+++ b/src/backend/access/common/detoast.c
@@ -497,6 +497,9 @@ toast_decompress_datum(struct varlena *attr)
  * Decompress the front of a compressed version of a varlena datum.
  * offset handling happens in detoast_attr_slice.
  * Here we just decompress a slice from the front.
+ *
+ * If slice decompression is not supported, the return datum is the
+ * decompression of the full datum.
  */
 static struct varlena *
 toast_decompress_datum_slice(struct varlena *attr, int32 slicelength)
diff --git a/src/backend/access/common/toast_compression.c b/src/backend/access/common/toast_compression.c
index a6f8b79a9e..080ddcf93c 100644
--- a/src/backend/access/common/toast_compression.c
+++ b/src/backend/access/common/toast_compression.c
@@ -203,6 +203,9 @@ lz4_decompress_datum(const struct varlena *value)
 
 /*
  * Decompress part of a varlena that was compressed using LZ4.
+ *
+ * If slice decompression is not supported, the return datum is the
+ * decompression of the full datum.
  */
 struct varlena *
 lz4_decompress_datum_slice(const struct varlena *value, int32 slicelength)