Index: libgo/go/runtime/os_aix.go
===================================================================
--- ./libgo/go/runtime/os_aix.go	(revision 259702)
+++ ./libgo/go/runtime/os_aix.go	(working copy)
@@ -61,12 +61,18 @@ func semasleep(ns int64) int32 {
 		if clock_gettime(CLOCK_REALTIME, &ts) != 0 {
 			throw("clock_gettime")
 		}
-		ts.tv_sec += timespec_sec_t(ns / 1000000000)
-		ts.tv_nsec += timespec_nsec_t(ns % 1000000000)
-		if ts.tv_nsec >= 1000000000 {
-			ts.tv_sec += timespec_sec_t(1)
-			ts.tv_nsec -= timespec_nsec_t(1000000000)
+		sec := int64(ts.tv_sec) + ns / 1000000000
+		nsec := int64(ts.tv_nsec) + ns % 1000000000
+		if nsec >= 1000000000 {
+			sec += 1
+			nsec -= 1000000000
 		}
+		if sec != int64(timespec_sec_t(sec)) {
+			// Handle overflows (timespec_sec_t is 32-bit in 32-bit applications)
+			sec = 1<<31 - 1
+		}
+		ts.tv_sec = timespec_sec_t(sec)
+		ts.tv_nsec = timespec_nsec_t(nsec)
 
 		if sem_timedwait((*semt)(unsafe.Pointer(_m_.mos.waitsema)), &ts) != 0 {
 			err := errno()