diff --git a/db/compaction.h b/db/compaction.h
index dc8712363..729c4edaf 100644
--- a/db/compaction.h
+++ b/db/compaction.h
@@ -138,6 +138,8 @@ class Compaction {
 
   // Clear all files to indicate that they are not being compacted
   // Delete this compaction from the list of running compactions.
+  //
+  // Requirement: DB mutex held
   void ReleaseCompactionFiles(Status status);
 
   // Returns the summary of the compaction in "output" with maximum "len"
diff --git a/db/compaction_picker.h b/db/compaction_picker.h
index b8611b4cb..0503c8692 100644
--- a/db/compaction_picker.h
+++ b/db/compaction_picker.h
@@ -83,6 +83,8 @@ class CompactionPicker {
 #endif  // ROCKSDB_LITE
 
   // Free up the files that participated in a compaction
+  //
+  // Requirement: DB mutex held
   void ReleaseCompactionFiles(Compaction* c, Status status);
 
   // Returns true if any one of the specified files are being compacted