diff --git a/examples/negative-after-op.ilo b/examples/negative-after-op.ilo
new file mode 100644
index 00000000..58b38be0
--- /dev/null
+++ b/examples/negative-after-op.ilo
@@ -0,0 +1,24 @@
+-- Negative literals immediately after a binary operator. The lexer eats
+-- `-0.05` as a single Number token, but a negative literal is itself a valid
+-- second operand to a binary op, so `<r -0.05` parses cleanly as
+-- `LessThan(r, -0.05)`. Same holds for negative literals in prefix-binary
+-- arg position (`+a -3`) and in call arg position (`mod n -2`).
+
+below x:n>n;<x -0.05{1}{0}
+shift a:n>n;+a -3
+modn n:n>n;mod n -2
+
+-- run: below -0.1
+-- out: 1
+-- run: below 0.1
+-- out: 0
+-- run: below -0.05
+-- out: 0
+-- run: shift 10
+-- out: 7
+-- run: shift -5
+-- out: -8
+-- run: modn 7
+-- out: 1
+-- run: modn 10
+-- out: 0
diff --git a/tests/regression_negative_literal_after_op.rs b/tests/regression_negative_literal_after_op.rs
new file mode 100644
index 00000000..02621971
--- /dev/null
+++ b/tests/regression_negative_literal_after_op.rs
@@ -0,0 +1,131 @@
+// Regression tests for negative numeric literals appearing immediately after
+// a binary operator or in a call/prefix-binop argument slot.
+//
+// The lexer eats a leading `-` as part of the Number token, so `<r -0.05`
+// produces tokens `Less, Ident(r), Number(-0.05)` rather than three tokens
+// for binary subtract. Multiple personas in real-world runs reported the
+// natural form `<r -0.05` parsing badly and had to rewrite it as
+// `nt=- 0 0.05; <r nt`. These tests pin the natural form across all engines:
+// a negative literal is itself a valid operand to a binary op, a prefix-binop
+// arg, and a function call arg.
+//
+// Variants exercised:
+//   - `<r -0.05{1}{0}` ternary against a negative threshold
+//   - `+a -3` prefix-binary add with a negative literal second operand
+//   - `mod n -2` builtin call with a negative literal arg
+//   - `id -1.5` ordinary function call with a negative literal arg
+
+use std::process::Command;
+
+fn ilo() -> Command {
+    Command::new(env!("CARGO_BIN_EXE_ilo"))
+}
+
+fn run(engine: &str, src: &str, args: &[&str]) -> String {
+    let mut cmd = ilo();
+    cmd.arg(src).arg(engine);
+    for a in args {
+        cmd.arg(a);
+    }
+    let out = cmd.output().expect("failed to run ilo");
+    assert!(
+        out.status.success(),
+        "ilo {engine} failed for `{src}` args={args:?}: stderr={}",
+        String::from_utf8_lossy(&out.stderr)
+    );
+    String::from_utf8_lossy(&out.stdout).trim().to_string()
+}
+
+const BELOW: &str = "f r:n>n;<r -0.05{1}{0}";
+const PREFIX_ADD: &str = "f a:n>n;+a -3";
+const MOD_NEG: &str = "f n:n>n;mod n -2";
+const ID_CALL: &str = "id x:n>n;x\nf>n;id -1.5\n";
+
+fn check_all(engine: &str) {
+    // `<r -0.05` ternary: r below the threshold returns 1, otherwise 0.
+    assert_eq!(
+        run(engine, BELOW, &["f", "-0.1"]),
+        "1",
+        "below: r=-0.1 engine={engine}"
+    );
+    assert_eq!(
+        run(engine, BELOW, &["f", "0.1"]),
+        "0",
+        "below: r=0.1 engine={engine}"
+    );
+    assert_eq!(
+        run(engine, BELOW, &["f", "-0.05"]),
+        "0",
+        "below: r=-0.05 (boundary, not strictly less) engine={engine}"
+    );
+
+    // Prefix-binary add with a negative literal second operand.
+    assert_eq!(
+        run(engine, PREFIX_ADD, &["f", "10"]),
+        "7",
+        "prefix-add: 10 + -3 engine={engine}"
+    );
+    assert_eq!(
+        run(engine, PREFIX_ADD, &["f", "-5"]),
+        "-8",
+        "prefix-add: -5 + -3 engine={engine}"
+    );
+
+    // Builtin call with a negative literal arg.
+    assert_eq!(
+        run(engine, MOD_NEG, &["f", "7"]),
+        "1",
+        "mod: 7 mod -2 engine={engine}"
+    );
+    assert_eq!(
+        run(engine, MOD_NEG, &["f", "10"]),
+        "0",
+        "mod: 10 mod -2 engine={engine}"
+    );
+}
+
+fn check_id(engine: &str) {
+    use std::sync::atomic::{AtomicU64, Ordering};
+    static COUNTER: AtomicU64 = AtomicU64::new(0);
+    let seq = COUNTER.fetch_add(1, Ordering::SeqCst);
+    let path = std::env::temp_dir().join(format!(
+        "ilo_neg_after_op_{}_{}_{}.ilo",
+        std::process::id(),
+        seq,
+        engine.trim_start_matches("--"),
+    ));
+    std::fs::write(&path, ID_CALL).unwrap();
+    let out = ilo()
+        .args([path.to_str().unwrap(), engine, "f"])
+        .output()
+        .expect("failed to run ilo");
+    assert!(
+        out.status.success(),
+        "ilo {engine} failed for id-call: stderr={}",
+        String::from_utf8_lossy(&out.stderr)
+    );
+    assert_eq!(
+        String::from_utf8_lossy(&out.stdout).trim(),
+        "-1.5",
+        "id-call: -1.5 round-trip engine={engine}"
+    );
+}
+
+#[test]
+fn neg_after_op_tree() {
+    check_all("--run-tree");
+    check_id("--run-tree");
+}
+
+#[test]
+fn neg_after_op_vm() {
+    check_all("--run-vm");
+    check_id("--run-vm");
+}
+
+#[test]
+#[cfg(feature = "cranelift")]
+fn neg_after_op_cranelift() {
+    check_all("--run-cranelift");
+    check_id("--run-cranelift");
+}