diff --git a/scheduler.go b/scheduler.go
index baafaa9..f51e0bd 100644
--- a/scheduler.go
+++ b/scheduler.go
@@ -537,6 +537,7 @@ func (s *Scheduler) EveryRandom(lower, upper int) *Scheduler {
 // Every schedules a new periodic Job with an interval.
 // Interval can be an int, time.Duration or a string that
 // parses with time.ParseDuration().
+// Negative intervals will return an error.
 // Valid time units are "ns", "us" (or "µs"), "ms", "s", "m", "h".
 //
 // The job is run immediately, unless:
@@ -553,6 +554,9 @@ func (s *Scheduler) Every(interval interface{}) *Scheduler {
 			job.error = wrapOrError(job.error, ErrInvalidInterval)
 		}
 	case time.Duration:
+		if interval <= 0 {
+			job.error = wrapOrError(job.error, ErrInvalidInterval)
+		}
 		job.setInterval(0)
 		job.setDuration(interval)
 		job.setUnit(duration)
@@ -561,6 +565,9 @@ func (s *Scheduler) Every(interval interface{}) *Scheduler {
 		if err != nil {
 			job.error = wrapOrError(job.error, err)
 		}
+		if d <= 0 {
+			job.error = wrapOrError(job.error, ErrInvalidInterval)
+		}
 		job.setDuration(d)
 		job.setUnit(duration)
 	default:
diff --git a/scheduler_test.go b/scheduler_test.go
index c5425fa..9edfbd8 100644
--- a/scheduler_test.go
+++ b/scheduler_test.go
@@ -82,8 +82,10 @@ func TestScheduler_Every_InvalidInterval(t *testing.T) {
 		interval      interface{}
 		expectedError string
 	}{
-		{"zero", 0, ErrInvalidInterval.Error()},
-		{"negative", -1, ErrInvalidInterval.Error()},
+		{"zero int", 0, ErrInvalidInterval.Error()},
+		{"negative int", -1, ErrInvalidInterval.Error()},
+		{"negative time.Duration", -1 * time.Millisecond, ErrInvalidInterval.Error()},
+		{"negative string duration", "-1ms", ErrInvalidInterval.Error()},
 		{"invalid string duration", "bad", "time: invalid duration \"bad\""},
 	}
 
@@ -93,7 +95,7 @@ func TestScheduler_Every_InvalidInterval(t *testing.T) {
 		t.Run(tc.description, func(t *testing.T) {
 			_, err := s.Every(tc.interval).Do(func() {})
 			require.Error(t, err)
-			assert.EqualError(t, err, tc.expectedError)
+			assert.ErrorContains(t, err, tc.expectedError)
 		})
 	}
 }