Mention that the append trick for copying fails on the empty slice
diff --git a/SliceTricks.md b/SliceTricks.md
index 2df9de2..f34a66e 100644
--- a/SliceTricks.md
+++ b/SliceTricks.md
@@ -11,7 +11,7 @@
 ```go
 b = make([]T, len(a))
 copy(b, a)
-// or
+// or, if a is not the empty slice,
 b = append([]T(nil), a...)
 ```