diff --git a/src/lib/builtins.pl b/src/lib/builtins.pl
index 786c56f25..bc91180ce 100644
--- a/src/lib/builtins.pl
+++ b/src/lib/builtins.pl
@@ -1410,24 +1410,34 @@
     ).
 
 number_chars(N, Chs) :-
-   (  ground(Chs)
-   -> can_be_number(N, number_chars/2),
-      can_be_list(Chs, number_chars/2),
-      '$chars_to_number'(Chs, Nx),
-      Nx = N
-   ;  must_be_number(N, number_chars/2),
-      (  var(Chs) -> true
-      ;  can_be_list(Chs, number_chars/2)
-      ,  chars_or_vars(Chs, number_chars/2)
-      ),
-      '$number_to_chars'(N, Chsx),
-      Chsx = Chs
+    (  ground(Chs) ->
+       can_be_number(N, number_chars/2),
+       catch(error:must_be(chars, Chs),
+             error(E, _),
+             builtins:throw(error(E, number_chars/2))
+            ),
+       '$chars_to_number'(Chs, Nx),
+       Nx = N
+    ;  must_be_number(N, number_chars/2),
+       (  var(Chs) -> true
+       ;  can_be_list(Chs, number_chars/2),
+          chars_or_vars(Chs, number_chars/2)
+       ),
+       '$number_to_chars'(N, Chsx),
+       Chsx = Chs
     ).
 
+list_of_ints(Ns) :-
+    error:must_be(list, Ns),
+    lists:maplist(error:must_be(integer), Ns).
+
 number_codes(N, Chs) :-
-   (  ground(Chs)
-   -> can_be_number(N, number_codes/2),
-      can_be_list(Chs, number_codes/2),
+   (  ground(Chs) ->
+      can_be_number(N, number_codes/2),
+      catch(builtins:list_of_ints(Chs),
+            error(E, _),
+            builtins:throw(error(E, number_codes/2))
+           ),
       '$codes_to_number'(Chs, Nx),
       Nx = N
    ;  must_be_number(N, number_codes/2),
@@ -1437,7 +1447,7 @@
       ),
       '$number_to_codes'(N, Chsx),
       Chsx = Chs
-    ).
+   ).
 
 subsumes_term(General, Specific) :-
    \+ \+ (
diff --git a/src/machine/system_calls.rs b/src/machine/system_calls.rs
index 2e016abd6..5f4cc32b9 100644
--- a/src/machine/system_calls.rs
+++ b/src/machine/system_calls.rs
@@ -1423,22 +1423,13 @@ impl Machine {
     pub(crate) fn chars_to_number(&mut self) -> CallResult {
         let stub_gen = || functor_stub(atom!("number_chars"), 2);
         let a1 = self.machine_st.store(self.machine_st.deref(self.machine_st.registers[1]));
+        let atom_or_string = self.machine_st.value_to_str_like(a1).unwrap();
 
-        if let Some(atom_or_string) = self.machine_st.value_to_str_like(a1) {
-            self.machine_st.parse_number_from_string(
-                atom_or_string.as_str(),
-                &self.indices,
-                stub_gen,
-            )?;
-        } else {
-            // a1 is a ground list at the call site within
-            // number_chars/2, so failure of value_to_str_like
-            // means the list contains a non-character.
-            let err = self.machine_st.type_error(ValidType::Character, a1);
-            return Err(self.machine_st.error_form(err, stub_gen()));
-        }
-
-        Ok(())
+        self.machine_st.parse_number_from_string(
+            atom_or_string.as_str(),
+            &self.indices,
+            stub_gen,
+        )
     }
 
     #[inline(always)]