diff --git a/tsdb/agent/db.go b/tsdb/agent/db.go
index e210cdc99e..71470a85df 100644
--- a/tsdb/agent/db.go
+++ b/tsdb/agent/db.go
@@ -317,13 +317,16 @@ func validateOptions(opts *Options) *Options {
 		opts.TruncateFrequency = DefaultTruncateFrequency
 	}
 	if opts.MinWALTime <= 0 {
-		opts.MinWALTime = 0
+		opts.MinWALTime = DefaultMinWALTime
 	}
 	if opts.MaxWALTime <= 0 {
 		opts.MaxWALTime = DefaultMaxWALTime
 	}
+	if opts.MinWALTime > opts.MaxWALTime {
+		opts.MaxWALTime = opts.MinWALTime
+	}
 
-	if t := int64(opts.TruncateFrequency * time.Hour / time.Millisecond); opts.MaxWALTime < t {
+	if t := int64(opts.TruncateFrequency / time.Millisecond); opts.MaxWALTime < t {
 		opts.MaxWALTime = t
 	}
 	return opts
diff --git a/tsdb/agent/db_test.go b/tsdb/agent/db_test.go
index 080913a866..9655533730 100644
--- a/tsdb/agent/db_test.go
+++ b/tsdb/agent/db_test.go
@@ -446,6 +446,25 @@ func Test_ExistingWAL_NextRef(t *testing.T) {
 	require.Equal(t, uint64(seriesCount), db.nextRef.Load(), "nextRef should be equal to the number of series written across the entire WAL")
 }
 
+func Test_validateOptions(t *testing.T) {
+	t.Run("Apply defaults to zero values", func(t *testing.T) {
+		opts := validateOptions(&Options{})
+		require.Equal(t, DefaultOptions(), opts)
+	})
+
+	t.Run("Defaults are already valid", func(t *testing.T) {
+		require.Equal(t, DefaultOptions(), validateOptions(nil))
+	})
+
+	t.Run("MaxWALTime should not be lower than TruncateFrequency", func(t *testing.T) {
+		opts := validateOptions(&Options{
+			MaxWALTime:        int64(time.Hour / time.Millisecond),
+			TruncateFrequency: 2 * time.Hour,
+		})
+		require.Equal(t, int64(2*time.Hour/time.Millisecond), opts.MaxWALTime)
+	})
+}
+
 func startTime() (int64, error) {
 	return time.Now().Unix() * 1000, nil
 }