diff --git a/src/runtime/debug_test.go b/src/runtime/debug_test.go
index 37dcafd145..f77a373d13 100644
--- a/src/runtime/debug_test.go
+++ b/src/runtime/debug_test.go
@@ -33,11 +33,17 @@ func startDebugCallWorker(t *testing.T) (g *runtime.G, after func()) {
 	skipUnderDebugger(t)
 
 	// This can deadlock if there aren't enough threads or if a GC
-	// tries to interrupt an atomic loop (see issue #10958).
-	ogomaxprocs := runtime.GOMAXPROCS(2)
+	// tries to interrupt an atomic loop (see issue #10958). We
+	// use 8 Ps so there's room for the debug call worker,
+	// something that's trying to preempt the call worker, and the
+	// goroutine that's trying to stop the call worker.
+	ogomaxprocs := runtime.GOMAXPROCS(8)
 	ogcpercent := debug.SetGCPercent(-1)
 
-	ready := make(chan *runtime.G)
+	// ready is a buffered channel so debugCallWorker won't block
+	// on sending to it. This makes it less likely we'll catch
+	// debugCallWorker while it's in the runtime.
+	ready := make(chan *runtime.G, 1)
 	var stop uint32
 	done := make(chan error)
 	go debugCallWorker(ready, &stop, done)
@@ -67,6 +73,10 @@ func debugCallWorker(ready chan<- *runtime.G, stop *uint32, done chan<- error) {
 	close(done)
 }
 
+// Don't inline this function, since we want to test adjusting
+// pointers in the arguments.
+//
+//go:noinline
 func debugCallWorker2(stop *uint32, x *int) {
 	for atomic.LoadUint32(stop) == 0 {
 		// Strongly encourage x to live in a register so we
@@ -193,7 +203,7 @@ func TestDebugCallUnsafePoint(t *testing.T) {
 
 	// This can deadlock if there aren't enough threads or if a GC
 	// tries to interrupt an atomic loop (see issue #10958).
-	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
 	defer debug.SetGCPercent(debug.SetGCPercent(-1))
 
 	// Test that the runtime refuses call injection at unsafe points.
@@ -215,7 +225,7 @@ func TestDebugCallPanic(t *testing.T) {
 	skipUnderDebugger(t)
 
 	// This can deadlock if there aren't enough threads.
-	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(2))
+	defer runtime.GOMAXPROCS(runtime.GOMAXPROCS(8))
 
 	ready := make(chan *runtime.G)
 	var stop uint32
diff --git a/src/runtime/export_debug_test.go b/src/runtime/export_debug_test.go
index 74f8855de6..e97dd52f20 100644
--- a/src/runtime/export_debug_test.go
+++ b/src/runtime/export_debug_test.go
@@ -50,19 +50,31 @@ func InjectDebugCall(gp *g, fn, args interface{}, tkill func(tid int) error) (in
 	h.gp = gp
 	h.fv, h.argp, h.argSize = fv, argp, argSize
 	h.handleF = h.handle // Avoid allocating closure during signal
-	noteclear(&h.done)
 
 	defer func() { testSigtrap = nil }()
-	testSigtrap = h.inject
-	if err := tkill(tid); err != nil {
-		return nil, err
+	for i := 0; ; i++ {
+		testSigtrap = h.inject
+		noteclear(&h.done)
+		h.err = ""
+
+		if err := tkill(tid); err != nil {
+			return nil, err
+		}
+		// Wait for completion.
+		notetsleepg(&h.done, -1)
+		if h.err != "" {
+			switch h.err {
+			case "retry _Grunnable", "executing on Go runtime stack":
+				// These are transient states. Try to get out of them.
+				if i < 100 {
+					Gosched()
+					continue
+				}
+			}
+			return nil, h.err
+		}
+		return h.panic, nil
 	}
-	// Wait for completion.
-	notetsleepg(&h.done, -1)
-	if len(h.err) != 0 {
-		return nil, h.err
-	}
-	return h.panic, nil
 }
 
 type debugCallHandler struct {
@@ -99,12 +111,18 @@ func (h *debugCallHandler) inject(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
 		h.savedRegs.fpstate = nil
 		// Set PC to debugCallV1.
 		ctxt.set_rip(uint64(funcPC(debugCallV1)))
+		// Call injected. Switch to the debugCall protocol.
+		testSigtrap = h.handleF
+	case _Grunnable:
+		// Ask InjectDebugCall to pause for a bit and then try
+		// again to interrupt this goroutine.
+		h.err = plainError("retry _Grunnable")
+		notewakeup(&h.done)
 	default:
 		h.err = plainError("goroutine in unexpected state at call inject")
-		return true
+		notewakeup(&h.done)
 	}
-	// Switch to the debugCall protocol and resume execution.
-	testSigtrap = h.handleF
+	// Resume execution.
 	return true
 }
 
@@ -149,6 +167,7 @@ func (h *debugCallHandler) handle(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
 		sp := ctxt.rsp()
 		reason := *(*string)(unsafe.Pointer(uintptr(sp)))
 		h.err = plainError(reason)
+		// Don't wake h.done. We need to transition to status 16 first.
 	case 16:
 		// Restore all registers except RIP and RSP.
 		rip, rsp := ctxt.rip(), ctxt.rsp()
@@ -162,6 +181,7 @@ func (h *debugCallHandler) handle(info *siginfo, ctxt *sigctxt, gp2 *g) bool {
 		notewakeup(&h.done)
 	default:
 		h.err = plainError("unexpected debugCallV1 status")
+		notewakeup(&h.done)
 	}
 	// Resume execution.
 	return true