diff --git a/tsdb/agent/db_test.go b/tsdb/agent/db_test.go
index 8bcb71c86a..cc5e0d34cb 100644
--- a/tsdb/agent/db_test.go
+++ b/tsdb/agent/db_test.go
@@ -524,6 +524,19 @@ func TestPartialTruncateWAL(t *testing.T) {
 		require.NoError(t, app.Commit())
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_histogram_batch-1", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		histograms := tsdbutil.GenerateTestCustomBucketsHistograms(numDatapoints)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, histograms[i], nil)
+			require.NoError(t, err)
+		}
+		require.NoError(t, app.Commit())
+	}
+
 	lbls = labelsForTest(t.Name()+"_float_histogram_batch-1", numSeries)
 	for _, l := range lbls {
 		lset := labels.New(l...)
@@ -537,6 +550,19 @@ func TestPartialTruncateWAL(t *testing.T) {
 		require.NoError(t, app.Commit())
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_float_histogram_batch-1", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		floatHistograms := tsdbutil.GenerateTestCustomBucketsFloatHistograms(numDatapoints)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, nil, floatHistograms[i])
+			require.NoError(t, err)
+		}
+		require.NoError(t, app.Commit())
+	}
+
 	// Create second batch of 800 series with 1000 data-points with a fixed lastTs as 600.
 	lastTs = 600
 	lbls = labelsForTest(t.Name()+"batch-2", numSeries)
@@ -563,6 +589,19 @@ func TestPartialTruncateWAL(t *testing.T) {
 		require.NoError(t, app.Commit())
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_histogram_batch-2", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		histograms := tsdbutil.GenerateTestCustomBucketsHistograms(numDatapoints)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, histograms[i], nil)
+			require.NoError(t, err)
+		}
+		require.NoError(t, app.Commit())
+	}
+
 	lbls = labelsForTest(t.Name()+"_float_histogram_batch-2", numSeries)
 	for _, l := range lbls {
 		lset := labels.New(l...)
@@ -576,11 +615,24 @@ func TestPartialTruncateWAL(t *testing.T) {
 		require.NoError(t, app.Commit())
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_float_histogram_batch-2", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		floatHistograms := tsdbutil.GenerateTestCustomBucketsFloatHistograms(numDatapoints)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, nil, floatHistograms[i])
+			require.NoError(t, err)
+		}
+		require.NoError(t, app.Commit())
+	}
+
 	// Truncate WAL with mint to GC only the first batch of 800 series and retaining 2nd batch of 800 series.
 	s.truncate(lastTs - 1)
 
 	m := gatherFamily(t, reg, "prometheus_agent_deleted_series")
-	require.Equal(t, float64(numSeries*3), m.Metric[0].Gauge.GetValue(), "agent wal truncate mismatch of deleted series count")
+	require.Equal(t, float64(numSeries*5), m.Metric[0].Gauge.GetValue(), "agent wal truncate mismatch of deleted series count")
 }
 
 func TestWALReplay(t *testing.T) {
@@ -616,6 +668,18 @@ func TestWALReplay(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_histogram", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		histograms := tsdbutil.GenerateTestCustomBucketsHistograms(numHistograms)
+
+		for i := 0; i < numHistograms; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, histograms[i], nil)
+			require.NoError(t, err)
+		}
+	}
+
 	lbls = labelsForTest(t.Name()+"_float_histogram", numSeries)
 	for _, l := range lbls {
 		lset := labels.New(l...)
@@ -628,6 +692,18 @@ func TestWALReplay(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_float_histogram", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		floatHistograms := tsdbutil.GenerateTestCustomBucketsFloatHistograms(numHistograms)
+
+		for i := 0; i < numHistograms; i++ {
+			_, err := app.AppendHistogram(0, lset, lastTs, nil, floatHistograms[i])
+			require.NoError(t, err)
+		}
+	}
+
 	require.NoError(t, app.Commit())
 	require.NoError(t, s.Close())
 
@@ -646,7 +722,7 @@ func TestWALReplay(t *testing.T) {
 
 	// Check if all the series are retrieved back from the WAL.
 	m := gatherFamily(t, reg, "prometheus_agent_active_series")
-	require.Equal(t, float64(numSeries*3), m.Metric[0].Gauge.GetValue(), "agent wal replay mismatch of active series count")
+	require.Equal(t, float64(numSeries*5), m.Metric[0].Gauge.GetValue(), "agent wal replay mismatch of active series count")
 
 	// Check if lastTs of the samples retrieved from the WAL is retained.
 	metrics := replayStorage.series.series
@@ -878,6 +954,18 @@ func TestDBAllowOOOSamples(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_histogram", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		histograms := tsdbutil.GenerateTestCustomBucketsHistograms(numHistograms)
+
+		for i := offset; i < numDatapoints+offset; i++ {
+			_, err := app.AppendHistogram(0, lset, int64(i), histograms[i-offset], nil)
+			require.NoError(t, err)
+		}
+	}
+
 	lbls = labelsForTest(t.Name()+"_float_histogram", numSeries)
 	for _, l := range lbls {
 		lset := labels.New(l...)
@@ -890,10 +978,22 @@ func TestDBAllowOOOSamples(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_float_histogram", numSeries)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		floatHistograms := tsdbutil.GenerateTestCustomBucketsFloatHistograms(numHistograms)
+
+		for i := offset; i < numDatapoints+offset; i++ {
+			_, err := app.AppendHistogram(0, lset, int64(i), nil, floatHistograms[i-offset])
+			require.NoError(t, err)
+		}
+	}
+
 	require.NoError(t, app.Commit())
 	m := gatherFamily(t, reg, "prometheus_agent_samples_appended_total")
 	require.Equal(t, float64(20), m.Metric[0].Counter.GetValue(), "agent wal mismatch of total appended samples")
-	require.Equal(t, float64(40), m.Metric[1].Counter.GetValue(), "agent wal mismatch of total appended histograms")
+	require.Equal(t, float64(80), m.Metric[1].Counter.GetValue(), "agent wal mismatch of total appended histograms")
 	require.NoError(t, s.Close())
 
 	// Hack: s.wal.Dir() is the /wal subdirectory of the original storage path.
@@ -942,6 +1042,18 @@ func TestDBAllowOOOSamples(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_histogram", numSeries*2)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		histograms := tsdbutil.GenerateTestCustomBucketsHistograms(numHistograms)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, int64(i), histograms[i], nil)
+			require.NoError(t, err)
+		}
+	}
+
 	lbls = labelsForTest(t.Name()+"_float_histogram", numSeries*2)
 	for _, l := range lbls {
 		lset := labels.New(l...)
@@ -954,10 +1066,22 @@ func TestDBAllowOOOSamples(t *testing.T) {
 		}
 	}
 
+	lbls = labelsForTest(t.Name()+"_custom_buckets_float_histogram", numSeries*2)
+	for _, l := range lbls {
+		lset := labels.New(l...)
+
+		floatHistograms := tsdbutil.GenerateTestCustomBucketsFloatHistograms(numHistograms)
+
+		for i := 0; i < numDatapoints; i++ {
+			_, err := app.AppendHistogram(0, lset, int64(i), nil, floatHistograms[i])
+			require.NoError(t, err)
+		}
+	}
+
 	require.NoError(t, app.Commit())
 	m = gatherFamily(t, reg2, "prometheus_agent_samples_appended_total")
 	require.Equal(t, float64(40), m.Metric[0].Counter.GetValue(), "agent wal mismatch of total appended samples")
-	require.Equal(t, float64(80), m.Metric[1].Counter.GetValue(), "agent wal mismatch of total appended histograms")
+	require.Equal(t, float64(160), m.Metric[1].Counter.GetValue(), "agent wal mismatch of total appended histograms")
 	require.NoError(t, db.Close())
 }