diff --git a/src/runtime/mgcmark.go b/src/runtime/mgcmark.go
index 6bc2d73d557..c4c922bda8d 100644
--- a/src/runtime/mgcmark.go
+++ b/src/runtime/mgcmark.go
@@ -258,6 +258,9 @@ func gcAssistAlloc(size uintptr, allowAssist bool) {
 // work is done here.
 //go:nowritebarrier
 func gcphasework(gp *g) {
+	if gp.gcworkdone {
+		return
+	}
 	switch gcphase {
 	default:
 		throw("gcphasework in bad gcphase")
diff --git a/src/runtime/stack1.go b/src/runtime/stack1.go
index f77e87cdf9c..5c2388d0e6f 100644
--- a/src/runtime/stack1.go
+++ b/src/runtime/stack1.go
@@ -743,8 +743,11 @@ func newstack() {
 		}
 		if gp.preemptscan {
 			for !castogscanstatus(gp, _Gwaiting, _Gscanwaiting) {
-				// Likely to be racing with the GC as it sees a _Gwaiting and does the stack scan.
-				// If so this stack will be scanned twice which does not change correctness.
+				// Likely to be racing with the GC as
+				// it sees a _Gwaiting and does the
+				// stack scan. If so, gcworkdone will
+				// be set and gcphasework will simply
+				// return.
 			}
 			gcphasework(gp)
 			casfrom_Gscanstatus(gp, _Gscanwaiting, _Gwaiting)