diff --git a/histogram/values.go b/histogram/values.go
index 3775fc2..99ba7c4 100644
--- a/histogram/values.go
+++ b/histogram/values.go
@@ -7,7 +7,12 @@ import (
 	"strings"
 )
 
-// StringifyValues turns
+// StringifyValues formats histogram values into a string.
+// The result is a comma-separated list of "value:count" pairs.
+// Each value is a non-negative int64 value, each count is a
+// greater or equal to 1 int.
+// If count is 1, the ":count" part is left out, so "42:1" and
+// "42" are sematically equal.
 func StringifyValues(values []int64) string {
 	n := len(values)
 	if n == 0 {
@@ -48,6 +53,10 @@ func StringifyValues(values []int64) string {
 	return strings.Join(toks, ",")
 }
 
+// ParseValues parses a "value:count" comma-separated
+// list of histogram values into a slice of int64 values.
+// The resulting slice contains each value ":count" times.
+// The resulting slice is sorted in ascending order.
 func ParseValues(s string) ([]int64, error) {
 	if s == "" {
 		return nil, nil
@@ -55,7 +64,7 @@ func ParseValues(s string) ([]int64, error) {
 	var values []int64
 	toks := strings.Split(s, ",")
 	for itok, tok := range toks {
-		v, c, err := parseValue(tok)
+		v, c, err := parseValueAndCount(tok)
 		if err != nil {
 			return nil, fmt.Errorf("cannot parse token #%d %q: %w", itok+1, tok, err)
 		}
@@ -70,7 +79,7 @@ func ParseValues(s string) ([]int64, error) {
 	return values, nil
 }
 
-func parseValue(s string) (int64, int, error) {
+func parseValueAndCount(s string) (int64, int, error) {
 	parts := strings.Split(s, ":")
 	np := len(parts)
 	if np < 1 || 2 < np {
diff --git a/histogram/values_test.go b/histogram/values_test.go
index d5962fa..4498151 100644
--- a/histogram/values_test.go
+++ b/histogram/values_test.go
@@ -1,6 +1,8 @@
 package histogram
 
 import (
+	"strconv"
+	"strings"
 	"testing"
 
 	"github.com/cvilsmeier/monibot-go/internal/assert"
@@ -17,33 +19,37 @@ func TestStringifyValues(t *testing.T) {
 }
 
 func TestParseValues(t *testing.T) {
-	strErr := func(err error) string {
-		if err == nil {
-			return "nil"
+	str := func(values []int64, err error) string {
+		if err != nil {
+			return err.Error()
 		}
-		return err.Error()
+		var ss []string
+		for _, v := range values {
+			ss = append(ss, strconv.FormatInt(v, 10))
+		}
+		return strings.Join(ss, ",")
 	}
 	ass := assert.New(t)
-	mustParse := func(s string) []int64 {
-		v, err := ParseValues(s)
-		ass.Nil(err)
-		return v
-	}
-	ass.Eq("", StringifyValues(mustParse("")))
-	ass.Eq("1", StringifyValues(mustParse("1")))
-	ass.Eq("1", StringifyValues(mustParse("1:1")))
-	ass.Eq("1:2", StringifyValues(mustParse("1:2")))
-	ass.Eq("1,2,3:2", StringifyValues(mustParse("3:2,2:1,1")))
-	_, err := ParseValues("-3:2")
-	ass.Eq("cannot parse token #1 \"-3:2\": invalid value -3", strErr(err))
-	_, err = ParseValues("-3:2")
-	ass.Eq("cannot parse token #1 \"-3:2\": invalid value -3", strErr(err))
-	_, err = ParseValues("3:0")
-	ass.Eq("cannot parse token #1 \"3:0\": invalid count 0", strErr(err))
-	_, err = ParseValues("foo")
-	ass.Eq("cannot parse token #1 \"foo\": cannot parse value \"foo\": strconv.ParseInt: parsing \"foo\": invalid syntax", strErr(err))
-	_, err = ParseValues("foo:1")
-	ass.Eq("cannot parse token #1 \"foo:1\": cannot parse value \"foo\": strconv.ParseInt: parsing \"foo\": invalid syntax", strErr(err))
-	_, err = ParseValues("1:foo")
-	ass.Eq("cannot parse token #1 \"1:foo\": cannot parse count \"foo\": strconv.Atoi: parsing \"foo\": invalid syntax", strErr(err))
+	v, err := ParseValues("")
+	ass.Eq("", str(v, err))
+	v, err = ParseValues("1")
+	ass.Eq("1", str(v, err))
+	v, err = ParseValues("1:1")
+	ass.Eq("1", str(v, err))
+	v, err = ParseValues("1:2")
+	ass.Eq("1,1", str(v, err))
+	v, err = ParseValues("3:2,2:1,1")
+	ass.Eq("1,2,3,3", str(v, err))
+	v, err = ParseValues("-3:2")
+	ass.Eq("cannot parse token #1 \"-3:2\": invalid value -3", str(v, err))
+	v, err = ParseValues("-3:2")
+	ass.Eq("cannot parse token #1 \"-3:2\": invalid value -3", str(v, err))
+	v, err = ParseValues("3:0")
+	ass.Eq("cannot parse token #1 \"3:0\": invalid count 0", str(v, err))
+	v, err = ParseValues("foo")
+	ass.Eq("cannot parse token #1 \"foo\": cannot parse value \"foo\": strconv.ParseInt: parsing \"foo\": invalid syntax", str(v, err))
+	v, err = ParseValues("foo:1")
+	ass.Eq("cannot parse token #1 \"foo:1\": cannot parse value \"foo\": strconv.ParseInt: parsing \"foo\": invalid syntax", str(v, err))
+	v, err = ParseValues("1:foo")
+	ass.Eq("cannot parse token #1 \"1:foo\": cannot parse count \"foo\": strconv.Atoi: parsing \"foo\": invalid syntax", str(v, err))
 }