diff --git a/pkg/brpb/brpb.pb.go b/pkg/brpb/brpb.pb.go
index a2d753481..350b44d68 100644
--- a/pkg/brpb/brpb.pb.go
+++ b/pkg/brpb/brpb.pb.go
@@ -4685,10 +4685,10 @@ func (m *LogFileSubcompactions) GetSubcompactions() []*LogFileSubcompaction {
 
 type LogFileCompaction struct {
 	// The selector of compaction source.
-	// Files contains ANY record greater than this will be selected.
+	// Files contains ANY record greater than this (and less than `until_ts`) will be selected.
 	CompactionFromTs uint64 `protobuf:"varint,1,opt,name=compaction_from_ts,json=compactionFromTs,proto3" json:"compaction_from_ts,omitempty"`
 	// The selector of compaction source.
-	// Files contains ANY record less than this will be selected.
+	// Files contains ANY record less than this (and not less than `until_ts`) will be selected.
 	CompactionUntilTs uint64 `protobuf:"varint,2,opt,name=compaction_until_ts,json=compactionUntilTs,proto3" json:"compaction_until_ts,omitempty"`
 	// The user provided name for the compaction.
 	Name string `protobuf:"bytes,3,opt,name=name,proto3" json:"name,omitempty"`
diff --git a/proto/brpb.proto b/proto/brpb.proto
index d39110731..050d57d98 100644
--- a/proto/brpb.proto
+++ b/proto/brpb.proto
@@ -853,10 +853,10 @@ message LogFileSubcompactions {
 
 message LogFileCompaction {
     // The selector of compaction source.
-    // Files contains ANY record greater than this will be selected.
+    // Files contains ANY record greater than this (and less than `until_ts`) will be selected.
     uint64 compaction_from_ts = 1;
     // The selector of compaction source.
-    // Files contains ANY record less than this will be selected.
+    // Files contains ANY record less than this (and not less than `until_ts`) will be selected.
     uint64 compaction_until_ts = 2;
     // The user provided name for the compaction.
     string name = 3;