diff --git a/src/runtime/netpoll.go b/src/runtime/netpoll.go
index 36b9edfe21..8d65a81edc 100644
--- a/src/runtime/netpoll.go
+++ b/src/runtime/netpoll.go
@@ -31,7 +31,7 @@ import (
 //     poll without blocking. If delta > 0, block for up to delta nanoseconds.
 //     Return a list of goroutines built by calling netpollready,
 //     and a delta to add to netpollWaiters when all goroutines are ready.
-//     This will never return an empty list with a non-zero delta.
+//     This must never return an empty list with a non-zero delta.
 //
 // func netpollBreak()
 //     Wake up the network poller, assumed to be blocked in netpoll.
diff --git a/src/runtime/netpoll_aix.go b/src/runtime/netpoll_aix.go
index 2df5a57111..4cf34d1c61 100644
--- a/src/runtime/netpoll_aix.go
+++ b/src/runtime/netpoll_aix.go
@@ -148,7 +148,10 @@ func netpollBreak() {
 }
 
 // netpoll checks for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
+//
 // delay < 0: blocks indefinitely
 // delay == 0: does not block, just polls
 // delay > 0: block for up to that many nanoseconds
diff --git a/src/runtime/netpoll_epoll.go b/src/runtime/netpoll_epoll.go
index ff6e0b5f89..c43bab0882 100644
--- a/src/runtime/netpoll_epoll.go
+++ b/src/runtime/netpoll_epoll.go
@@ -89,7 +89,10 @@ func netpollBreak() {
 }
 
 // netpoll checks for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
+//
 // delay < 0: blocks indefinitely
 // delay == 0: does not block, just polls
 // delay > 0: block for up to that many nanoseconds
diff --git a/src/runtime/netpoll_kqueue.go b/src/runtime/netpoll_kqueue.go
index 6cd80d5c30..ca7898205e 100644
--- a/src/runtime/netpoll_kqueue.go
+++ b/src/runtime/netpoll_kqueue.go
@@ -80,7 +80,10 @@ func netpollBreak() {
 }
 
 // netpoll checks for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
+//
 // delay < 0: blocks indefinitely
 // delay == 0: does not block, just polls
 // delay > 0: block for up to that many nanoseconds
diff --git a/src/runtime/netpoll_solaris.go b/src/runtime/netpoll_solaris.go
index fddc29000b..90459c08df 100644
--- a/src/runtime/netpoll_solaris.go
+++ b/src/runtime/netpoll_solaris.go
@@ -215,7 +215,10 @@ func netpollBreak() {
 }
 
 // netpoll checks for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
+//
 // delay < 0: blocks indefinitely
 // delay == 0: does not block, just polls
 // delay > 0: block for up to that many nanoseconds
diff --git a/src/runtime/netpoll_stub.go b/src/runtime/netpoll_stub.go
index c1bda3fa8b..dc5d708b4c 100644
--- a/src/runtime/netpoll_stub.go
+++ b/src/runtime/netpoll_stub.go
@@ -32,7 +32,9 @@ func netpollBreak() {
 }
 
 // Polls for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
 func netpoll(delay int64) (gList, int32) {
 	// Implementation for platforms that do not support
 	// integrated network poller.
diff --git a/src/runtime/netpoll_windows.go b/src/runtime/netpoll_windows.go
index c3c10af723..fb35d41c0c 100644
--- a/src/runtime/netpoll_windows.go
+++ b/src/runtime/netpoll_windows.go
@@ -144,7 +144,10 @@ func netpollBreak() {
 }
 
 // netpoll checks for ready network connections.
-// Returns list of goroutines that become runnable.
+// Returns a list of goroutines that become runnable,
+// and a delta to add to netpollWaiters.
+// This must never return an empty list with a non-zero delta.
+//
 // delay < 0: blocks indefinitely
 // delay == 0: does not block, just polls
 // delay > 0: block for up to that many nanoseconds