diff --git a/src/backend/access/common/detoast.c b/src/backend/access/common/detoast.c
index a7f7a47478..545a6b8867 100644
--- a/src/backend/access/common/detoast.c
+++ b/src/backend/access/common/detoast.c
@@ -506,6 +506,17 @@ toast_decompress_datum_slice(struct varlena *attr, int32 slicelength)
 
 	Assert(VARATT_IS_COMPRESSED(attr));
 
+	/*
+	 * Some callers may pass a slicelength that's more than the actual
+	 * decompressed size.  If so, just decompress normally.  This avoids
+	 * possibly allocating a larger-than-necessary result object, and may be
+	 * faster and/or more robust as well.  Notably, some versions of liblz4
+	 * have been seen to give wrong results if passed an output size that is
+	 * more than the data's true decompressed size.
+	 */
+	if ((uint32) slicelength >= TOAST_COMPRESS_EXTSIZE(attr))
+		return toast_decompress_datum(attr);
+
 	/*
 	 * Fetch the compression method id stored in the compression header and
 	 * decompress the data slice using the appropriate decompression routine.
diff --git a/src/include/access/toast_internals.h b/src/include/access/toast_internals.h
index bf118f0482..1c28b07c4d 100644
--- a/src/include/access/toast_internals.h
+++ b/src/include/access/toast_internals.h
@@ -31,6 +31,8 @@ typedef struct toast_compress_header
  * Utilities for manipulation of header information for compressed
  * toast entries.
  */
+#define TOAST_COMPRESS_EXTSIZE(ptr) \
+	(((toast_compress_header *) (ptr))->tcinfo & VARLENA_EXTSIZE_MASK)
 #define TOAST_COMPRESS_METHOD(ptr) \
 	(((toast_compress_header *) (ptr))->tcinfo >> VARLENA_EXTSIZE_BITS)