diff --git a/src/runtime/netpoll.go b/src/runtime/netpoll.go
index 2393711..1008b44 100644
--- a/src/runtime/netpoll.go
+++ b/src/runtime/netpoll.go
@@ -78,6 +78,7 @@
 	// pollReset, pollWait, pollWaitCanceled and runtime·netpollready (IO readiness notification)
 	// proceed w/o taking the lock. So closing, everr, rg, rd, wg and wd are manipulated
 	// in a lock-free way by all operations.
+	// TODO(golang.org/issue/49008): audit these lock-free fields for continued correctness.
 	// NOTE(dvyukov): the following code uses uintptr to store *g (rg/wg),
 	// that will blow up when GC starts moving objects.
 	lock    mutex // protects the following fields
@@ -86,11 +87,11 @@
 	everr   bool      // marks event scanning error happened
 	user    uint32    // user settable cookie
 	rseq    uintptr   // protects from stale read timers
-	rg      uintptr   // pdReady, pdWait, G waiting for read or nil
+	rg      uintptr   // pdReady, pdWait, G waiting for read or nil. Accessed atomically.
 	rt      timer     // read deadline timer (set if rt.f != nil)
 	rd      int64     // read deadline
 	wseq    uintptr   // protects from stale write timers
-	wg      uintptr   // pdReady, pdWait, G waiting for write or nil
+	wg      uintptr   // pdReady, pdWait, G waiting for write or nil. Accessed atomically.
 	wt      timer     // write deadline timer
 	wd      int64     // write deadline
 	self    *pollDesc // storage for indirect interface. See (*pollDesc).makeArg.
@@ -147,20 +148,22 @@
 func poll_runtime_pollOpen(fd uintptr) (*pollDesc, int) {
 	pd := pollcache.alloc()
 	lock(&pd.lock)
-	if pd.wg != 0 && pd.wg != pdReady {
+	wg := atomic.Loaduintptr(&pd.wg)
+	if wg != 0 && wg != pdReady {
 		throw("runtime: blocked write on free polldesc")
 	}
-	if pd.rg != 0 && pd.rg != pdReady {
+	rg := atomic.Loaduintptr(&pd.rg)
+	if rg != 0 && rg != pdReady {
 		throw("runtime: blocked read on free polldesc")
 	}
 	pd.fd = fd
 	pd.closing = false
 	pd.everr = false
 	pd.rseq++
-	pd.rg = 0
+	atomic.Storeuintptr(&pd.rg, 0)
 	pd.rd = 0
 	pd.wseq++
-	pd.wg = 0
+	atomic.Storeuintptr(&pd.wg, 0)
 	pd.wd = 0
 	pd.self = pd
 	unlock(&pd.lock)
@@ -178,10 +181,12 @@
 	if !pd.closing {
 		throw("runtime: close polldesc w/o unblock")
 	}
-	if pd.wg != 0 && pd.wg != pdReady {
+	wg := atomic.Loaduintptr(&pd.wg)
+	if wg != 0 && wg != pdReady {
 		throw("runtime: blocked write on closing polldesc")
 	}
-	if pd.rg != 0 && pd.rg != pdReady {
+	rg := atomic.Loaduintptr(&pd.rg)
+	if rg != 0 && rg != pdReady {
 		throw("runtime: blocked read on closing polldesc")
 	}
 	netpollclose(pd.fd)
@@ -205,9 +210,9 @@
 		return errcode
 	}
 	if mode == 'r' {
-		pd.rg = 0
+		atomic.Storeuintptr(&pd.rg, 0)
 	} else if mode == 'w' {
-		pd.wg = 0
+		atomic.Storeuintptr(&pd.wg, 0)
 	}
 	return pollNoError
 }
@@ -417,6 +422,8 @@
 
 // returns true if IO is ready, or false if timedout or closed
 // waitio - wait only for completed IO, ignore errors
+// Concurrent calls to netpollblock in the same mode are forbidden, as pollDesc
+// can hold only a single waiting goroutine for each mode.
 func netpollblock(pd *pollDesc, mode int32, waitio bool) bool {
 	gpp := &pd.rg
 	if mode == 'w' {
@@ -425,17 +432,19 @@
 
 	// set the gpp semaphore to pdWait
 	for {
-		old := *gpp
-		if old == pdReady {
-			*gpp = 0
+		// Consume notification if already ready.
+		if atomic.Casuintptr(gpp, pdReady, 0) {
 			return true
 		}
-		if old != 0 {
-			throw("runtime: double wait")
-		}
 		if atomic.Casuintptr(gpp, 0, pdWait) {
 			break
 		}
+
+		// Double check that this isn't corrupt; otherwise we'd loop
+		// forever.
+		if v := atomic.Loaduintptr(gpp); v != pdReady && v != 0 {
+			throw("runtime: double wait")
+		}
 	}
 
 	// need to recheck error states after setting gpp to pdWait
@@ -459,7 +468,7 @@
 	}
 
 	for {
-		old := *gpp
+		old := atomic.Loaduintptr(gpp)
 		if old == pdReady {
 			return nil
 		}