diff --git a/fish-rust/src/common.rs b/fish-rust/src/common.rs
index 73e76a0c8..7725e6e2f 100644
--- a/fish-rust/src/common.rs
+++ b/fish-rust/src/common.rs
@@ -979,6 +979,9 @@ pub fn read_unquoted_escape(
     }
 
     if let Some(c) = result_char_or_none {
+        if fish_reserved_codepoint(c) {
+            return None;
+        }
         result.push(c);
     }
 
@@ -1134,9 +1137,7 @@ pub fn str2wcstring(inp: &[u8]) -> WString {
                 Some(codepoint) => {
                     c = codepoint;
                     // Determine whether to encode this character with our crazy scheme.
-                    (c >= ENCODE_DIRECT_BASE && c < ENCODE_DIRECT_END)
-                    ||
-                    c == INTERNAL_SEPARATOR
+                    fish_reserved_codepoint(c)
                     ||
                     // Incomplete sequence.
                     ret == 0_usize.wrapping_sub(2)
diff --git a/src/common.cpp b/src/common.cpp
index 60319dfed..f12c47ed2 100644
--- a/src/common.cpp
+++ b/src/common.cpp
@@ -328,12 +328,10 @@ 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) {
+            if (fish_reserved_codepoint(wc)) {
                 use_encode_direct = true;
             } else if ((wc >= 0xD800 && wc <= 0xDFFF) || static_cast<uint32_t>(wc) >= 0x110000) {
                 use_encode_direct = true;
-            } else if (wc == INTERNAL_SEPARATOR) {
-                use_encode_direct = true;
             } else if (ret == static_cast<size_t>(-2)) {
                 // Incomplete sequence.
                 use_encode_direct = true;
diff --git a/tests/checks/basic.fish b/tests/checks/basic.fish
index 9d913de6c..eedc04035 100644
--- a/tests/checks/basic.fish
+++ b/tests/checks/basic.fish
@@ -612,6 +612,14 @@ $fish -c begin
 echo $status
 # CHECK: 127
 
+$fish -c 'echo \ufdd2"fart"'
+# CHECKERR: fish: Invalid token '\ufdd2"fart"'
+# CHECKERR: echo \ufdd2"fart"
+# CHECKERR: ^~~~~~~~~~~^
+
+echo (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