diff --git a/src/common.cpp b/src/common.cpp
index a1cc7c63c..370ecacd5 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -335,9 +335,7 @@ static wcstring str2wcs_internal(const char *in, const size_t in_len) {
         } else {
             ret = std::mbrtowc(&wc, &in[in_pos], in_len - in_pos, &state);
             // Determine whether to encode this character with our crazy scheme.
-            if (wc >= ENCODE_DIRECT_BASE && wc < ENCODE_DIRECT_BASE + 256) {
-                use_encode_direct = true;
-            } else if (wc == INTERNAL_SEPARATOR) {
+            if (fish_reserved_codepoint(wc)) {
                 use_encode_direct = true;
             } else if (ret == static_cast<size_t>(-2)) {
                 // Incomplete sequence.
@@ -1313,6 +1311,9 @@ maybe_t<size_t> read_unquoted_escape(const wchar_t *input, wcstring *result, boo
     }
 
     if (result_char_or_none.has_value()) {
+        if (fish_reserved_codepoint(*result_char_or_none)) {
+            return none();
+        }
         result->push_back(*result_char_or_none);
     }
 
diff --git a/tests/checks/basic.fish b/tests/checks/basic.fish
index 60a4e18a2..314b78cc0 100644
--- a/tests/checks/basic.fish
+++ b/tests/checks/basic.fish
@@ -587,6 +587,14 @@ $fish -c 'echo \x'
 # CHECKERR: echo \x
 # CHECKERR:      ^^
 
+$fish -c 'echo \ufdd2"fart"'
+# CHECKERR: fish: Invalid token '\ufdd2"fart"'
+# CHECKERR: echo \ufdd2"fart"
+# CHECKERR: ^~~~~~~~~~~^
+
+echo (sh -c 'printf $\'\ufdd2foo\'') | string escape
+# CHECK: \Xef\Xb7\X92foo
+
 printf '%s\n' "#!/bin/sh" 'echo $0' > $tmpdir/argv0.sh
 chmod +x $tmpdir/argv0.sh
 cd $tmpdir