diff --git a/prometheus/histogram.go b/prometheus/histogram.go
index e43898c63..727bec42a 100644
--- a/prometheus/histogram.go
+++ b/prometheus/histogram.go
@@ -1886,16 +1886,16 @@ func validateExemplars(exemplars []*dto.Exemplar) error {
 //
 // zeroBucket counts all (positive and negative)
 // observations in the zero bucket (with an absolute value less or equal
-// the current threshold)
+// the current threshold).
 // positiveBuckets and negativeBuckets are separate maps for negative and positive
 // observations. The map's value is an int64, counting observations in
 // that bucket. The map's key is the
 // index of the bucket according to the used
-// Schema. Index 0 is for an upper bound of 1.
+// Schema. Index 0 is for an upper bound of 1 in positive buckets and for a lower bound of -1 in negative buckets.
 // NewConstNativeHistogram returns an error if
-// 1.the length of labelValues is not consistent with the variable labels in Desc or if Desc is invalid.
-// 2.the schema passed is not between 8 and -4
-// 3.the sum of counts in the bucket do not equal count
+// - the length of labelValues is not consistent with the variable labels in Desc or if Desc is invalid.
+// - the schema passed is not between 8 and -4
+// - the sum of counts in the bucket do not equal count when sum  is not Nan
 func NewConstNativeHistogram(
 	desc *Desc,
 	count uint64,