diff --git a/src/runtime/mgc.go b/src/runtime/mgc.go
index 4b9a6da3b3..5c565a5853 100644
--- a/src/runtime/mgc.go
+++ b/src/runtime/mgc.go
@@ -409,7 +409,8 @@ type gcControllerState struct {
 }
 
 // startCycle resets the GC controller's state and computes estimates
-// for a new GC cycle. The caller must hold worldsema.
+// for a new GC cycle. The caller must hold worldsema and the world
+// must be stopped.
 func (c *gcControllerState) startCycle() {
 	c.scanWork = 0
 	c.bgScanCredit = 0
@@ -499,7 +500,7 @@ func (c *gcControllerState) revise() {
 
 	// Assume we're under the soft goal. Pace GC to complete at
 	// next_gc assuming the heap is in steady-state.
-	heapGoal := int64(memstats.next_gc)
+	heapGoal := int64(atomic.Load64(&memstats.next_gc))
 
 	// Compute the expected scan work remaining.
 	//
@@ -512,12 +513,12 @@ func (c *gcControllerState) revise() {
 	// 100*heap_scan.)
 	scanWorkExpected := int64(float64(scan) * 100 / float64(100+gcpercent))
 
-	if live > memstats.next_gc || work > scanWorkExpected {
+	if int64(live) > heapGoal || work > scanWorkExpected {
 		// We're past the soft goal, or we've already done more scan
 		// work than we expected. Pace GC so that in the worst case it
 		// will complete by the hard goal.
 		const maxOvershoot = 1.1
-		heapGoal = int64(float64(memstats.next_gc) * maxOvershoot)
+		heapGoal = int64(float64(heapGoal) * maxOvershoot)
 
 		// Compute the upper bound on the scan work remaining.
 		scanWorkExpected = int64(scan)
@@ -846,7 +847,7 @@ func gcSetTriggerRatio(triggerRatio float64) {
 
 	// Commit to the trigger and goal.
 	memstats.gc_trigger = trigger
-	memstats.next_gc = goal
+	atomic.Store64(&memstats.next_gc, goal)
 	if trace.enabled {
 		traceNextGC()
 	}
@@ -903,7 +904,7 @@ func gcSetTriggerRatio(triggerRatio float64) {
 //
 // mheap_.lock must be held or the world must be stopped.
 func gcEffectiveGrowthRatio() float64 {
-	egogc := float64(memstats.next_gc-memstats.heap_marked) / float64(memstats.heap_marked)
+	egogc := float64(atomic.Load64(&memstats.next_gc)-memstats.heap_marked) / float64(memstats.heap_marked)
 	if egogc < 0 {
 		// Shouldn't happen, but just in case.
 		egogc = 0
diff --git a/src/runtime/mgcscavenge.go b/src/runtime/mgcscavenge.go
index 34646828e5..6328b295ca 100644
--- a/src/runtime/mgcscavenge.go
+++ b/src/runtime/mgcscavenge.go
@@ -123,7 +123,7 @@ func gcPaceScavenger() {
 		return
 	}
 	// Compute our scavenging goal.
-	goalRatio := float64(memstats.next_gc) / float64(memstats.last_next_gc)
+	goalRatio := float64(atomic.Load64(&memstats.next_gc)) / float64(memstats.last_next_gc)
 	retainedGoal := uint64(float64(memstats.last_heap_inuse) * goalRatio)
 	// Add retainExtraPercent overhead to retainedGoal. This calculation
 	// looks strange but the purpose is to arrive at an integer division
diff --git a/src/runtime/mstats.go b/src/runtime/mstats.go
index 2c217ecf84..8cc20552fb 100644
--- a/src/runtime/mstats.go
+++ b/src/runtime/mstats.go
@@ -57,9 +57,15 @@ type mstats struct {
 	gc_sys       uint64 // updated atomically or during STW
 	other_sys    uint64 // updated atomically or during STW
 
-	// Statistics about garbage collector.
+	// Statistics about the garbage collector.
+
+	// next_gc is the goal heap_live for when next GC ends.
+	// Set to ^uint64(0) if disabled.
+	//
+	// Read and written atomically, unless the world is stopped.
+	next_gc uint64
+
 	// Protected by mheap or stopping the world during GC.
-	next_gc         uint64 // goal heap_live for when next GC ends; ^0 if disabled
 	last_gc_unix    uint64 // last gc (in unix time)
 	pause_total_ns  uint64
 	pause_ns        [256]uint64 // circular buffer of recent gc pause lengths
diff --git a/src/runtime/trace.go b/src/runtime/trace.go
index 169b650eb4..d3ecd148be 100644
--- a/src/runtime/trace.go
+++ b/src/runtime/trace.go
@@ -13,6 +13,7 @@
 package runtime
 
 import (
+	"runtime/internal/atomic"
 	"runtime/internal/sys"
 	"unsafe"
 )
@@ -1146,11 +1147,11 @@ func traceHeapAlloc() {
 }
 
 func traceNextGC() {
-	if memstats.next_gc == ^uint64(0) {
+	if nextGC := atomic.Load64(&memstats.next_gc); nextGC == ^uint64(0) {
 		// Heap-based triggering is disabled.
 		traceEvent(traceEvNextGC, -1, 0)
 	} else {
-		traceEvent(traceEvNextGC, -1, memstats.next_gc)
+		traceEvent(traceEvNextGC, -1, nextGC)
 	}
 }