diff --git a/entry.go b/entry.go
index 9ae900b..89e966e 100644
--- a/entry.go
+++ b/entry.go
@@ -68,7 +68,7 @@
 
 // Add a map of fields to the Entry.
 func (entry *Entry) WithFields(fields Fields) *Entry {
-	data := Fields{}
+	data := make(Fields, len(entry.Data)+len(fields))
 	for k, v := range entry.Data {
 		data[k] = v
 	}