diff --git a/crates/simplexpr/src/parser/lexer.rs b/crates/simplexpr/src/parser/lexer.rs
index 34b0ed6..ce9919c 100644
--- a/crates/simplexpr/src/parser/lexer.rs
+++ b/crates/simplexpr/src/parser/lexer.rs
@@ -166,7 +166,7 @@ impl<'s> Lexer<'s> {
 
                 let tok_str = &self.source[self.pos..self.pos + len];
                 let old_pos = self.pos;
-                self.advance_by(len);
+                self.advance_by(len)?;
                 match LEXER_FNS[i](tok_str.to_string()) {
                     Token::Skip | Token::Comment => {}
                     token => {
@@ -177,11 +177,17 @@ impl<'s> Lexer<'s> {
         }
     }
 
-    fn advance_by(&mut self, n: usize) {
+    /// Advance position by the given number of characters, respecting char boundaries. Returns `None` when n exceeds the source length
+    #[must_use]
+    fn advance_by(&mut self, n: usize) -> Option<()> {
+        if self.pos + n > self.source.len() {
+            return None;
+        }
         self.pos += n;
         while self.pos < self.source.len() && !self.source.is_char_boundary(self.pos) {
             self.pos += 1;
         }
+        Some(())
     }
 
     fn advance_until_one_of<'a>(&mut self, pat: &[&'a str]) -> Option<&'a str> {
@@ -190,10 +196,10 @@ impl<'s> Lexer<'s> {
             if remaining.is_empty() {
                 return None;
             } else if let Some(matched) = pat.iter().find(|&&p| remaining.starts_with(p)) {
-                self.advance_by(matched.len());
+                self.advance_by(matched.len())?;
                 return Some(matched);
             } else {
-                self.advance_by(1);
+                self.advance_by(1)?;
             }
         }
     }
@@ -203,7 +209,7 @@ impl<'s> Lexer<'s> {
         pattern.push("\\");
         match self.advance_until_one_of(pattern.as_slice()) {
             Some("\\") => {
-                self.advance_by(1);
+                self.advance_by(1)?;
                 self.advance_until_unescaped_one_of(pat)
             }
             result => result,
@@ -213,7 +219,7 @@ impl<'s> Lexer<'s> {
     pub fn string_lit(&mut self) -> Option<Result<Sp<Vec<Sp<StrLitSegment>>>, LexicalError>> {
         let quote = self.remaining().chars().next()?.to_string();
         let str_lit_start = self.pos;
-        self.advance_by(quote.len());
+        self.advance_by(quote.len())?;
 
         let mut elements = Vec::new();
         let mut in_string_lit = true;
@@ -308,6 +314,7 @@ mod test {
     snapshot_string! {
         basic                 => v!(r#"bar "foo""#),
         digit                 => v!(r#"12"#),
+        quote_backslash_eof   => v!(r#""\"#),
         number_in_ident       => v!(r#"foo_1_bar"#),
         interpolation_1       => v!(r#" "foo ${2 * 2} bar" "#),
         interpolation_nested  => v!(r#" "foo ${(2 * 2) + "${5 + 5}"} bar" "#),
diff --git a/crates/simplexpr/src/parser/snapshots/simplexpr__parser__lexer__test__quote_backslash_eof.snap b/crates/simplexpr/src/parser/snapshots/simplexpr__parser__lexer__test__quote_backslash_eof.snap
new file mode 100644
index 0000000..cd7f646
--- /dev/null
+++ b/crates/simplexpr/src/parser/snapshots/simplexpr__parser__lexer__test__quote_backslash_eof.snap
@@ -0,0 +1,6 @@
+---
+source: crates/simplexpr/src/parser/lexer.rs
+assertion_line: 313
+expression: "v!(r#\"\"\\\"#)"
+---
+