diff --git a/package/origlang-compiler/src/lexer.rs b/package/origlang-compiler/src/lexer.rs
index 932567b5..e8108995 100644
--- a/package/origlang-compiler/src/lexer.rs
+++ b/package/origlang-compiler/src/lexer.rs
@@ -300,7 +300,7 @@ impl Lexer<'_> {
             let r = self.byte_skip_n(plus);
 
             if let Ok(b) = r {
-                if (b'0'..b'9').contains(&b) {
+                if (b'0'..=b'9').contains(&b) {
                     plus += 1;
                 } else {
                     break
diff --git a/package/origlang-compiler/src/lexer/tests.rs b/package/origlang-compiler/src/lexer/tests.rs
index 01e6faef..d5ffc82a 100644
--- a/package/origlang-compiler/src/lexer/tests.rs
+++ b/package/origlang-compiler/src/lexer/tests.rs
@@ -217,3 +217,19 @@ fn crlf_negative() {
         char: '\r',
     });
 }
+
+#[test]
+fn off_by_one_range_regression() {
+    const S: &str = "9";
+    let lexer = Lexer::create(S);
+    assert_eq!(lexer.next(), Pointed {
+        data: Token::Digits {
+            sequence: "9".to_string(),
+            suffix: None,
+        },
+        position: SourcePosition {
+            line: NonZeroUsize::new(1).unwrap(),
+            column: NonZeroUsize::new(1).unwrap(),
+        }
+    })
+}
\ No newline at end of file