diff --git a/norm.go b/norm.go
index 3371922..7ba6ad7 100644
--- a/norm.go
+++ b/norm.go
@@ -19,5 +19,5 @@ func (n Norm) Jitter(d time.Duration) time.Duration {
 	}
 
 	samp := f()*float64(n.Stdev) + float64(n.Mean)
-	return d * time.Duration(samp)
+	return d + time.Duration(samp)
 }
diff --git a/univariate.go b/univariate.go
index ea1ffa4..dc7fdcf 100644
--- a/univariate.go
+++ b/univariate.go
@@ -16,5 +16,5 @@ type Univariate struct {
 
 // Jitter the duration by drawing from a univariate distribution
 func (u Univariate) Jitter(d time.Duration) time.Duration {
-	return d * time.Duration(u.Rand())
+	return d + time.Duration(u.Rand())
 }