diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index c7d6d8a55c2e3..07c75677d0532 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -965,8 +965,9 @@ impl Default for Rc<CStr> {
     /// This may or may not share an allocation with other Rcs on the same thread.
     #[inline]
     fn default() -> Self {
-        let c_str: &CStr = Default::default();
-        Rc::from(c_str)
+        let rc = Rc::<[u8]>::from(*b"\0");
+        // `[u8]` has the same layout as `CStr`, and it is `NUL` terminated.
+        unsafe { Rc::from_raw(Rc::into_raw(rc) as *const CStr) }
     }
 }
 
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index ae3318b839dd7..05e76ccf685e1 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -2369,7 +2369,9 @@ impl Default for Rc<str> {
     /// This may or may not share an allocation with other Rcs on the same thread.
     #[inline]
     fn default() -> Self {
-        Rc::from("")
+        let rc = Rc::<[u8]>::default();
+        // `[u8]` has the same layout as `str`.
+        unsafe { Rc::from_raw(Rc::into_raw(rc) as *const str) }
     }
 }