diff --git a/serde_json/src/de.rs b/serde_json/src/de.rs
index 8dea69e1..04491899 100644
--- a/serde_json/src/de.rs
+++ b/serde_json/src/de.rs
@@ -259,7 +259,9 @@ impl<Iter> Deserializer<Iter>
                 if pos {
                     visitor.visit_u64(res)
                 } else {
-                    let res_i64 = (res as i64).wrapping_neg();
+                    // FIXME: `wrapping_neg` will be stable in Rust 1.2
+                    //let res_i64 = (res as i64).wrapping_neg();
+                    let res_i64 = (!res + 1) as i64;
 
                     // Convert into a float if we underflow.
                     if res_i64 > 0 {