diff --git a/prometheus/counter.go b/prometheus/counter.go
index 00d70f09b..de30de6da 100644
--- a/prometheus/counter.go
+++ b/prometheus/counter.go
@@ -51,7 +51,7 @@ type Counter interface {
 // will lead to a valid (label-less) exemplar. But if Labels is nil, the current
 // exemplar is left in place. AddWithExemplar panics if the value is < 0, if any
 // of the provided labels are invalid, or if the provided labels contain more
-// than 64 runes in total.
+// than 128 runes in total.
 type ExemplarAdder interface {
 	AddWithExemplar(value float64, exemplar Labels)
 }
diff --git a/prometheus/observer.go b/prometheus/observer.go
index 44128016f..03773b21f 100644
--- a/prometheus/observer.go
+++ b/prometheus/observer.go
@@ -58,7 +58,7 @@ type ObserverVec interface {
 // current time as timestamp, and the provided Labels. Empty Labels will lead to
 // a valid (label-less) exemplar. But if Labels is nil, the current exemplar is
 // left in place. ObserveWithExemplar panics if any of the provided labels are
-// invalid or if the provided labels contain more than 64 runes in total.
+// invalid or if the provided labels contain more than 128 runes in total.
 type ExemplarObserver interface {
 	ObserveWithExemplar(value float64, exemplar Labels)
 }