diff --git a/src/runtime/malloc.go b/src/runtime/malloc.go
index f827b9c418f..ea1dd6ea499 100644
--- a/src/runtime/malloc.go
+++ b/src/runtime/malloc.go
@@ -395,6 +395,14 @@ func gcwork(force int32) {
 		gctimer.cycle.markterm = nanotime()
 		systemstack(stoptheworld)
 		systemstack(gcinstalloffwb_m)
+	} else {
+		// For non-concurrent GC (force != 0) g stack have not been scanned so
+		// set gcscanvalid such that mark termination scans all stacks.
+		// No races here since we are in a STW phase.
+		for _, gp := range allgs {
+			gp.gcworkdone = false  // set to true in gcphasework
+			gp.gcscanvalid = false // stack has not been scanned
+		}
 	}
 
 	startTime := nanotime()
diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 8cc060c2cf5..67ecd3a806f 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -587,7 +587,10 @@ func markroot(desc *parfor, i uint32) {
 		}
 
 		// Shrink a stack if not much of it is being used but not in the scan phase.
-		if gcphase != _GCscan { // Do not shrink during GCscan phase.
+		if gcphase == _GCmarktermination {
+			// Shrink during STW GCmarktermination phase thus avoiding
+			// complications introduced by shrinking during
+			// non-STW phases.
 			shrinkstack(gp)
 		}
 		if readgstatus(gp) == _Gdead {
@@ -853,6 +856,9 @@ func scanframe(frame *stkframe, unused unsafe.Pointer) bool {
 
 //go:nowritebarrier
 func scanstack(gp *g) {
+	if gp.gcscanvalid {
+		return
+	}
 
 	if readgstatus(gp)&_Gscan == 0 {
 		print("runtime:scanstack: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", hex(readgstatus(gp)), "\n")
@@ -882,6 +888,7 @@ func scanstack(gp *g) {
 
 	gentraceback(^uintptr(0), ^uintptr(0), 0, gp, 0, nil, 0x7fffffff, scanframe, nil, 0)
 	tracebackdefers(gp, scanframe, nil)
+	gp.gcscanvalid = true
 }
 
 // Shade the object if it isn't already.
@@ -945,6 +952,7 @@ func gcphasework(gp *g) {
 	case _GCscan:
 		// scan the stack, mark the objects, put pointers in work buffers
 		// hanging off the P where this is being run.
+		// Indicate that the scan is valid until the goroutine runs again
 		scanstack(gp)
 	case _GCmark:
 		// No work.
@@ -1455,7 +1463,8 @@ func gcscan_m() {
 	local_allglen := allglen
 	for i := uintptr(0); i < local_allglen; i++ {
 		gp := allgs[i]
-		gp.gcworkdone = false // set to true in gcphasework
+		gp.gcworkdone = false  // set to true in gcphasework
+		gp.gcscanvalid = false // stack has not been scanned
 	}
 	unlock(&allglock)
 
diff --git a/src/runtime/proc1.go b/src/runtime/proc1.go
index fcff60541de..8efb5467be0 100644
--- a/src/runtime/proc1.go
+++ b/src/runtime/proc1.go
@@ -345,6 +345,9 @@ func casfrom_Gscanstatus(gp *g, oldval, newval uint32) {
 		dumpgstatus(gp)
 		throw("casfrom_Gscanstatus: gp->status is not in scan state")
 	}
+	if newval == _Grunning {
+		gp.gcscanvalid = false
+	}
 }
 
 // This will return false if the gp is not in the expected status and the cas fails.
@@ -358,6 +361,10 @@ func castogscanstatus(gp *g, oldval, newval uint32) bool {
 			return cas(&gp.atomicstatus, oldval, newval)
 		}
 	case _Grunning:
+		if gp.gcscanvalid {
+			print("runtime: castogscanstatus _Grunning and gp.gcscanvalid is true, newval=", hex(newval), "\n")
+			throw("castogscanstatus")
+		}
 		if newval == _Gscanrunning || newval == _Gscanenqueue {
 			return cas(&gp.atomicstatus, oldval, newval)
 		}
@@ -375,11 +382,15 @@ func castogscanstatus(gp *g, oldval, newval uint32) bool {
 func casgstatus(gp *g, oldval, newval uint32) {
 	if (oldval&_Gscan != 0) || (newval&_Gscan != 0) || oldval == newval {
 		systemstack(func() {
-			print("casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n")
+			print("runtime: casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n")
 			throw("casgstatus: bad incoming values")
 		})
 	}
 
+	if newval == _Grunning {
+		gp.gcscanvalid = false
+	}
+
 	// loop if gp->atomicstatus is in a scan state giving
 	// GC time to finish and change the state to oldval.
 	for !cas(&gp.atomicstatus, oldval, newval) {
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index c71a3c31435..6935fcd826b 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -203,6 +203,7 @@ type g struct {
 	paniconfault bool // panic (instead of crash) on unexpected fault address
 	preemptscan  bool // preempted g does scan for gc
 	gcworkdone   bool // debug: cleared at begining of gc work phase cycle, set by gcphasework, tested at end of cycle
+	gcscanvalid  bool // false at start of gc cycle, true if G has not run since last scan
 	throwsplit   bool // must not split stack
 	raceignore   int8 // ignore race detection events
 	m            *m   // for debuggers, but offset not hard-coded