diff --git a/opentelemetry/proto/metrics/v1/metrics.proto b/opentelemetry/proto/metrics/v1/metrics.proto
index ac5a3a472..f631ee829 100644
--- a/opentelemetry/proto/metrics/v1/metrics.proto
+++ b/opentelemetry/proto/metrics/v1/metrics.proto
@@ -403,25 +403,44 @@ message SummaryDataPoint {
   // Value is UNIX Epoch time in nanoseconds since 00:00:00 UTC on 1 January 1970.
   fixed64 time_unix_nano = 3;
 
-  // The total number of recorded values since start_time. Optional since
-  // some systems don't expose this.
+  // The total number of recorded values since start_time.  This field
+  // MUST be omitted when its true value is 1.  An omitted or zero
+  // value is interpreted as having `count` equal to 1, and in this
+  // case the value of `sum`, `min`, and `max` are implied to equal
+  // the value of `last`.
   uint64 count = 4;
 
-  // The total sum of recorded values since start_time. Optional since some
-  // systems don't expose this. If count is zero then this field must be zero.
+  // The last value MUST be set to the last value that was measured
+  // since start_time.
+  double last = 7;
+
+  // The total sum of recorded values since start_time.  If the count
+  // was omitted or zero because its true value was 1, this field
+  // shall be omitted by the writer and the value of `sum` shall be
+  // set by the reader to value of `last`.  Otherwise, this field MUST
+  // be set to the sum of measurements reflected in count.
   double sum = 5;
 
-  // Represents the value at a given percentile of a distribution.
-  //
-  // To record Min and Max values following conventions are used:
-  // - The 100th percentile is equivalent to the maximum value observed.
-  // - The 0th percentile is equivalent to the minimum value observed.
-  //
-  // See the following issue for more context:
-  // https://github.com/open-telemetry/opentelemetry-proto/issues/125
+  // The minimum of recorded values since start_time.  If the count
+  // was omitted or zero because its true value was 1, this field
+  // shall be omitted by the writer and the value of `min` shall be
+  // set by the reader to value of `last`.  Otherwise, this field MUST
+  // be set to the minimum of the measurements reflected in count.
+  double min = 8;
+
+  // The maximum of recorded values since start_time.  If the count
+  // was omitted or zero because its true value was 1, this field
+  // shall be omitted by the writer and the value of `max` shall be
+  // set by the reader to value of `last`.  Otherwise, this field MUST
+  // be set to the maximum of the measurements reflected in count.
+  double max = 9;
+
+  // Represents the value at a given percentile of a distribution.  To
+  // represent the maximum or minimum values, use `max` and `min`
+  // fields, do not use percentiles 0 or 100.
   message ValueAtPercentile {
     // The percentile of a distribution. Must be in the interval
-    // [0.0, 100.0].
+    // (0.0, 100.0).
     double percentile = 1;
 
     // The value at the given percentile of a distribution.