diff --git a/src/builtins/function.rs b/src/builtins/function.rs
index 4bf4a81b2..28b64a4f8 100644
--- a/src/builtins/function.rs
+++ b/src/builtins/function.rs
@@ -92,6 +92,14 @@ fn parse_cmd_opts(
                 // A positional argument we got because we use RETURN_IN_ORDER.
                 let woptarg = w.woptarg.unwrap().to_owned();
                 if handling_named_arguments {
+                    if is_read_only(&woptarg) {
+                        streams.err.append(wgettext_fmt!(
+                            "%ls: variable '%ls' is read-only\n",
+                            cmd,
+                            woptarg
+                        ));
+                        return STATUS_INVALID_ARGS;
+                    }
                     opts.named_arguments.push(woptarg);
                 } else {
                     streams.err.append(wgettext_fmt!(
diff --git a/tests/checks/function.fish b/tests/checks/function.fish
index bf71723be..058a036d3 100644
--- a/tests/checks/function.fish
+++ b/tests/checks/function.fish
@@ -183,6 +183,11 @@ function foo --argument-names status; end
 echo status $status
 # CHECK: status 2
 
+function foo --argument-names foo status; end
+# CHECKERR: {{.*}}function.fish (line {{\d+}}): function: variable 'status' is read-only
+# CHECKERR: function foo --argument-names foo status; end
+# CHECKERR: ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
+
 functions -q foo
 echo exists $status
 # CHECK: exists 1