diff --git a/src/pkg/runtime/time.goc b/src/pkg/runtime/time.goc
index 1101ad068a0..b575696f715 100644
--- a/src/pkg/runtime/time.goc
+++ b/src/pkg/runtime/time.goc
@@ -13,8 +13,13 @@ package time
 #include "malloc.h"
 #include "race.h"
 
+enum {
+	debug = 0,
+};
+
 static Timers timers;
 static void addtimer(Timer*);
+static void dumptimers(int8*);
 
 // Package time APIs.
 // Godoc uses the comments in package time, not these.
@@ -92,6 +97,11 @@ addtimer(Timer *t)
 	int32 n;
 	Timer **nt;
 
+	// when must never be negative; otherwise timerproc will overflow
+	// during its delta calculation and never expire other timers.
+	if(t->when < 0)
+		t->when = (1LL<<63)-1;
+
 	if(timers.len >= timers.cap) {
 		// Grow slice.
 		n = 16;
@@ -121,6 +131,8 @@ addtimer(Timer *t)
 		timers.timerproc = runtime·newproc1(&timerprocv, nil, 0, 0, addtimer);
 		timers.timerproc->issystem = true;
 	}
+	if(debug)
+		dumptimers("addtimer");
 }
 
 // Delete timer t from the heap.
@@ -157,6 +169,8 @@ runtime·deltimer(Timer *t)
 		siftup(i);
 		siftdown(i);
 	}
+	if(debug)
+		dumptimers("deltimer");
 	runtime·unlock(&timers);
 	return true;
 }
@@ -285,3 +299,18 @@ siftdown(int32 i)
 		i = c;
 	}
 }
+
+static void
+dumptimers(int8 *msg)
+{
+	Timer *t;
+	int32 i;
+
+	runtime·printf("timers: %s\n", msg);
+	for(i = 0; i < timers.len; i++) {
+		t = timers.t[i];
+		runtime·printf("\t%d\t%p:\ti %d when %D period %D fn %p\n",
+				i, t, t->i, t->when, t->period, t->fv->fn);
+	}
+	runtime·printf("\n");
+}
diff --git a/src/pkg/time/internal_test.go b/src/pkg/time/internal_test.go
index 918a9f33be6..4e5557d6a0b 100644
--- a/src/pkg/time/internal_test.go
+++ b/src/pkg/time/internal_test.go
@@ -4,6 +4,11 @@
 
 package time
 
+import (
+	"errors"
+	"runtime"
+)
+
 func init() {
 	// force US/Pacific for time zone tests
 	ForceUSPacificForTesting()
@@ -11,3 +16,61 @@ func init() {
 
 var Interrupt = interrupt
 var DaysIn = daysIn
+
+func empty(now int64, arg interface{}) {}
+
+// Test that a runtimeTimer with a duration so large it overflows
+// does not cause other timers to hang.
+//
+// This test has to be in internal_test.go since it fiddles with
+// unexported data structures.
+func CheckRuntimeTimerOverflow() error {
+	// We manually create a runtimeTimer to bypass the overflow
+	// detection logic in NewTimer: we're testing the underlying
+	// runtime.addtimer function.
+	r := &runtimeTimer{
+		when: nano() + (1<<63 - 1),
+		f:    empty,
+		arg:  nil,
+	}
+	startTimer(r)
+
+	const timeout = 100 * Millisecond
+
+	// Start a goroutine that should send on t.C before the timeout.
+	t := NewTimer(1)
+
+	defer func() {
+		// Subsequent tests won't work correctly if we don't stop the
+		// overflow timer and kick the timer proc back into service.
+		//
+		// The timer proc is now sleeping and can only be awoken by
+		// adding a timer to the *beginning* of the heap. We can't
+		// wake it up by calling NewTimer since other tests may have
+		// left timers running that should have expired before ours.
+		// Instead we zero the overflow timer duration and start it
+		// once more.
+		stopTimer(r)
+		t.Stop()
+		r.when = 0
+		startTimer(r)
+	}()
+
+	// Try to receive from t.C before the timeout. It will succeed
+	// iff the previous sleep was able to finish. We're forced to
+	// spin and yield after trying to receive since we can't start
+	// any more timers (they might hang due to the same bug we're
+	// now testing).
+	stop := Now().Add(timeout)
+	for {
+		select {
+		case <-t.C:
+			return nil // It worked!
+		default:
+			if Now().After(stop) {
+				return errors.New("runtime timer stuck: overflow in addtimer")
+			}
+			runtime.Gosched()
+		}
+	}
+}
diff --git a/src/pkg/time/sleep_test.go b/src/pkg/time/sleep_test.go
index d21b9cca44a..46872595094 100644
--- a/src/pkg/time/sleep_test.go
+++ b/src/pkg/time/sleep_test.go
@@ -396,3 +396,9 @@ func TestIssue5745(t *testing.T) {
 	timer.Stop()
 	t.Error("Should be unreachable.")
 }
+
+func TestOverflowRuntimeTimer(t *testing.T) {
+	if err := CheckRuntimeTimerOverflow(); err != nil {
+		t.Fatalf(err.Error())
+	}
+}