diff --git a/src/runtime/proc1.go b/src/runtime/proc1.go
index e3565a6d33..2786e7e441 100644
--- a/src/runtime/proc1.go
+++ b/src/runtime/proc1.go
@@ -158,7 +158,15 @@ func ready(gp *g, traceskip int) {
 // readyExecute marks gp ready to run, preempt the current g, and execute gp.
 // This is used to start concurrent GC promptly when we reach its trigger.
 func readyExecute(gp *g, traceskip int) {
+	// Squirrel away gp so we don't allocate a closure for the
+	// mcall'd func below. If we allocate a closure, it could go
+	// away as soon as we put _g_ on the runqueue.
+	getg().readyg = gp
+
 	mcall(func(_g_ *g) {
+		gp := _g_.readyg
+		_g_.readyg = nil
+
 		if trace.enabled {
 			traceGoUnpark(gp, traceskip)
 			traceGoSched()
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 609c7cf6f6..3230d4e1a8 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -243,6 +243,7 @@ type g struct {
 	startpc      uintptr // pc of goroutine function
 	racectx      uintptr
 	waiting      *sudog // sudog structures this g is waiting on (that have a valid elem ptr)
+	readyg       *g     // scratch for readyExecute
 }
 
 type mts struct {
diff --git a/src/runtime/stubs.go b/src/runtime/stubs.go
index 7b6fbb0349..50e2a207da 100644
--- a/src/runtime/stubs.go
+++ b/src/runtime/stubs.go
@@ -33,7 +33,10 @@ func getg() *g
 // run other goroutines.
 //
 // mcall can only be called from g stacks (not g0, not gsignal).
-//go:noescape
+//
+// This must NOT be go:noescape: if fn is a stack-allocated closure,
+// fn puts g on a run queue, and g executes before fn returns, the
+// closure will be invalidated while it is still executing.
 func mcall(fn func(*g))
 
 // systemstack runs fn on a system stack.