diff --git a/tape/dynamic.go b/tape/dynamic.go
index 2528ace..bded11f 100644
--- a/tape/dynamic.go
+++ b/tape/dynamic.go
@@ -129,7 +129,7 @@ func decodeAny(decoder *Decoder, destination reflect.Value, tag Tag) (n int, err
 			return n, errWrongDestinationType("slice")
 		}
 		if destination.Cap() < int(length) {
-			destination.Grow(destination.Cap() - int(length))
+			destination.Grow(int(length) - destination.Cap())
 		}
 		destination.SetLen(int(length))
 		for index := range length {