diff --git a/src/runtime/mprof.go b/src/runtime/mprof.go
index 45f107722a..937194a238 100644
--- a/src/runtime/mprof.go
+++ b/src/runtime/mprof.go
@@ -39,7 +39,10 @@ const (
 	// size of bucket hash table
 	buckHashSize = 179999
 
-	// max depth of stack to record in bucket
+	// maxStack is the max depth of stack to record in bucket.
+	// Note that it's only used internally as a guard against
+	// wildly out-of-bounds slicing of the PCs that come after
+	// a bucket struct, and it could increase in the future.
 	maxStack = 32
 )
 
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 2a02e1fb3b..885b493bad 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -583,7 +583,7 @@ type m struct {
 	alllink       *m // on allm
 	schedlink     muintptr
 	lockedg       guintptr
-	createstack   [32]uintptr // stack that created this thread.
+	createstack   [32]uintptr // stack that created this thread, it's used for StackRecord.Stack0, so it must align with it.
 	lockedExt     uint32      // tracking for external LockOSThread
 	lockedInt     uint32      // tracking for internal lockOSThread
 	nextwaitm     muintptr    // next m waiting for lock