diff --git a/numpy/_core/src/umath/loops.c.src b/numpy/_core/src/umath/loops.c.src
index 3928d2a0d0c4..141676a8a768 100644
--- a/numpy/_core/src/umath/loops.c.src
+++ b/numpy/_core/src/umath/loops.c.src
@@ -687,8 +687,9 @@ NPY_NO_EXPORT void
 TIMEDELTA_sign(char **args, npy_intp const *dimensions, npy_intp const *steps, void *NPY_UNUSED(func))
 {
     UNARY_LOOP {
+        /* Sign of NaT is NaT */
         const npy_timedelta in1 = *(npy_timedelta *)ip1;
-        *((npy_timedelta *)op1) = in1 > 0 ? 1 : (in1 < 0 ? -1 : 0);
+        *((npy_timedelta *)op1) = in1 == NPY_DATETIME_NAT ? NPY_DATETIME_NAT : (in1 > 0 ? 1 : (in1 < 0 ? -1 : 0));
     }
 }