diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index ade4d11433..d75af10206 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -3474,7 +3474,7 @@ func sysmon() {
 		}
 		// check if we need to force a GC
 		lastgc := int64(atomic.Load64(&memstats.last_gc))
-		if lastgc != 0 && unixnow-lastgc > forcegcperiod && atomic.Load(&forcegc.idle) != 0 {
+		if gcphase == _GCoff && lastgc != 0 && unixnow-lastgc > forcegcperiod && atomic.Load(&forcegc.idle) != 0 {
 			lock(&forcegc.lock)
 			forcegc.idle = 0
 			forcegc.g.schedlink = 0