diff --git a/opentelemetry/proto/metrics/v1/metrics.proto b/opentelemetry/proto/metrics/v1/metrics.proto
index 7c092e8e5..c7604c31e 100644
--- a/opentelemetry/proto/metrics/v1/metrics.proto
+++ b/opentelemetry/proto/metrics/v1/metrics.proto
@@ -155,25 +155,55 @@ message MetricDescriptor {
   repeated string label_keys = 5;
 }
 
+// LabelValues is a list of label string values.
+message LabelValues {
+  // Values of labels. Each element in this array is the value of the key defined at the
+  // corresponding index of MetricDescriptor.label_keys array. The number of elements
+  // in these 2 arrays must be the same. Note that values array must include empty
+  // strings and must also contain an empty string value for labels for which the
+  // value was originally unspecified.
+  repeated string values = 1;
+
+  // Some metric sources allow setting the value of a label to be equal not just to
+  // empty string but to an unspecified value, or in other words the value of a particular
+  // label defined in label_keys array may be missing in a particular timeseries.
+  // In order to support this concept and because ProtoBuf cannot distinguish empty string
+  // from unspecified string we store indexes of unspecified labels in "values" array in
+  // this field. This field contains only indexes of unspecified labels.
+  // This field should not contain duplicate numbers, numbers less than zero or
+  // numbers greater than or equal to the length of values array.
+  repeated int32 unspecified_value_indexes = 2;
+
+  // For example:
+  //   label_keys = {"a",      "b",             "c", "d", "e"}
+  //   values =     {"value1", "another value", "",  "",  "yet another string"}
+  //   unspecified_value_indexes = {2}
+  // Because unspecified_value_indexes field contains value 2 it means that the empty
+  // string at index 3 of values array must be interpreted as unspecified value and
+  // not as an empty string, which means label "c" has no value. As opposed to that
+  // empty value at index 3 is treated as normal empty string so label "d" has
+  // value of empty string.
+}
+
 // Int64TimeSeries is a list of data points that describes the time-varying values
 // of a int64 metric.
 message Int64TimeSeries {
   // The set of label values that uniquely identify this timeseries. Applies to
   // all points. The order of label values must match that of label keys in the
   // metric descriptor.
-  repeated LabelValue label_values = 1;
+  LabelValues label_values = 1;
 
   // The data points of this timeseries.
   repeated Int64Value points = 2;
 }
 
-// eDoubleTimeSeries is a list of data points that describes the time-varying values
+// DoubleTimeSeries is a list of data points that describes the time-varying values
 // of a double metric.
 message DoubleTimeSeries {
   // The set of label values that uniquely identify this timeseries. Applies to
   // all points. The order of label values must match that of label keys in the
   // metric descriptor.
-  repeated LabelValue label_values = 1;
+  LabelValues label_values = 1;
 
   // The data points of this timeseries.
   repeated DoubleValue points = 2;
@@ -185,7 +215,7 @@ message HistogramTimeSeries {
   // The set of label values that uniquely identify this timeseries. Applies to
   // all points. The order of label values must match that of label keys in the
   // metric descriptor.
-  repeated LabelValue label_values = 1;
+  LabelValues label_values = 1;
 
   // The data points of this timeseries.
   repeated HistogramValue points = 2;
@@ -228,21 +258,12 @@ message SummaryTimeSeries {
   // The set of label values that uniquely identify this timeseries. Applies to
   // all points. The order of label values must match that of label keys in the
   // metric descriptor.
-  repeated LabelValue label_values = 1;
+  LabelValues label_values = 1;
 
   // The data points of this timeseries.
   repeated SummaryValue points = 2;
 }
 
-// Label value or indication that the value is missing
-message LabelValue {
-  // The value for the label.
-  string value = 1;
-  // If false the value field is ignored and considered not set.
-  // This is used to differentiate a missing label from an empty string.
-  bool has_value = 2;
-}
-
 // Int64Value is a timestamped measurement of int64 value.
 message Int64Value {
   // start_time_unixnano is the time when the cumulative value was reset to zero.