Make possible lossy conversion explicit.
diff --git a/src/core/support/sync_posix.c b/src/core/support/sync_posix.c
index d6a0f7c..4d59a10 100644
--- a/src/core/support/sync_posix.c
+++ b/src/core/support/sync_posix.c
@@ -81,7 +81,7 @@
   } else {
     struct timespec abs_deadline_ts;
     abs_deadline = gpr_convert_clock_type(abs_deadline, GPR_CLOCK_REALTIME);
-    abs_deadline_ts.tv_sec = abs_deadline.tv_sec;
+    abs_deadline_ts.tv_sec = (time_t)abs_deadline.tv_sec;
     abs_deadline_ts.tv_nsec = abs_deadline.tv_nsec;
     err = pthread_cond_timedwait(cv, mu, &abs_deadline_ts);
   }