diff --git a/bps.go b/bps.go
index ff40761..0138b3e 100644
--- a/bps.go
+++ b/bps.go
@@ -133,7 +133,7 @@ func (b *BPS) HumanRate() string {
 
 // Sparkline returns a human-friendly sprakline of history
 func (b *BPS) Sparkline(count int) string {
-	if count > len(b.buckets) {
+	if count <= 0 || count > len(b.buckets) {
 		return "bucket count inappropriate"
 	}
 	sparks := []string{"▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"}
@@ -147,9 +147,12 @@ func (b *BPS) Sparkline(count int) string {
 
 	// find max
 	for i := 0; i < len(b.buckets); i++ {
-		cur = b.buckets[i]
-		if cur > max {
-			max = cur
+		cur += b.buckets[i]
+		if i%bucketsPer == 0 {
+			if cur > max {
+				max = cur
+			}
+			cur = 0
 		}
 	}
 
diff --git a/bps_test.go b/bps_test.go
index df9057e..7d6bb14 100644
--- a/bps_test.go
+++ b/bps_test.go
@@ -94,32 +94,67 @@ func TestHumanBytes(t *testing.T) {
 	}
 }
 
-func TestSparkline(t *testing.T) {
+// TestSparkBadBucketCounts just makes sure that bad inputs are reported
+func TestSparkBadBucketCounts(t *testing.T) {
 	bw := BPS{
 		buckets: make([]int64, 10),
 	}
-	t.Logf("%+v", bw.Sparkline(100))
+	sizes := []int{-10, -1, 0, 11, 12, 100, 1000}
+	for _, size := range sizes {
+		got := bw.Sparkline(size)
+		want := "bucket count inappropriate"
+		if got != want {
+			t.Fatalf("got: %v, want: %v", got, want)
+		}
+	}
+}
+
+// TestSparkline just creates a simple BPS and traverses all reasonable count
+// sizes. It's primarily a test for panics which plagued us early on.
+func TestSparkline(t *testing.T) {
+	buckets := 20
+	bw := BPS{
+		buckets: make([]int64, buckets),
+	}
+
+	t.Logf("all 0")
+	for i := 0; i < buckets; i++ {
+		bw.buckets[i] = 0
+	}
+	for i := 1; i < buckets; i++ {
+		line := bw.Sparkline(i)
+		t.Logf("count: %d, len %d: %+v", i, len([]rune(line)), line)
+	}
+
+	t.Logf("increasing")
+	for i := 0; i < buckets; i++ {
+		bw.buckets[i] = int64(i * buckets)
+	}
+	for i := 1; i < buckets; i++ {
+		line := bw.Sparkline(i)
+		t.Logf("count: %d, len %d: %+v", i, len([]rune(line)), line)
+	}
+
+	t.Logf("decreasing")
+	for i := 0; i < buckets; i++ {
+		bw.buckets[i] = int64((buckets - i) * buckets)
+	}
+	for i := 1; i < buckets; i++ {
+		line := bw.Sparkline(i)
+		t.Logf("count: %d, len %d: %+v", i, len([]rune(line)), line)
+	}
+}
+
+func TestSparkRandom(t *testing.T) {
+	buckets := 20
+	bw := BPS{
+		buckets: make([]int64, buckets),
+	}
 	bw.buckets[3] = 100
 	t.Logf("%+v", bw.Sparkline(10))
 	bw.buckets[7] = 300
-	for i := 1; i < 10; i++ {
-		t.Logf("%+v", bw.Sparkline(i))
+	for i := 1; i < buckets; i++ {
+		line := bw.Sparkline(i)
+		t.Logf("count: %d, len: %d: %+v", i, len([]rune(line)), line)
 	}
-
-	for i := 0; i < 10; i++ {
-		bw.buckets[i] = int64(i * 10)
-		t.Logf("%+v", bw.Sparkline(10))
-	}
-	t.Logf("%+v", bw.Sparkline(10))
-	for i := 0; i < 10; i++ {
-		bw.buckets[i] = 0
-	}
-
-	for i := 0; i < 10; i++ {
-		bw.buckets[i] = int64((10 - i) * 10)
-		t.Logf("%+v", bw.Sparkline(10))
-	}
-	t.Logf("%+v", bw.Sparkline(10))
-	bw.buckets[5] = 200
-	t.Logf("%+v", bw.Sparkline(10))
 }