diff --git a/Python/pytime.c b/Python/pytime.c
index a7eda86..0d28911 100644
--- a/Python/pytime.c
+++ b/Python/pytime.c
@@ -360,6 +360,8 @@
 
     if (res && raise)
         _PyTime_overflow();
+
+    assert(0 <= tv->tv_usec && tv->tv_usec <= 999999);
     return res;
 }
 
@@ -393,6 +395,8 @@
         return -1;
     }
     ts->tv_nsec = nsec;
+
+    assert(0 <= ts->tv_nsec && ts->tv_nsec <= 999999999);
     return 0;
 }
 #endif