diff --git a/argus/src/parser/lexer.rs b/argus/src/parser/lexer.rs
index 1caf017..ddd3ae3 100644
--- a/argus/src/parser/lexer.rs
+++ b/argus/src/parser/lexer.rs
@@ -98,15 +98,27 @@ pub fn lexer<'src>() -> impl Parser<'src, &'src str, Output<'src>, Error<'src>>
         // .then(frac.or_not())
         // .then(exp.or_not())
         .to_slice()
-        .map(|s: &str| Token::Float(s.parse().unwrap()))
+        .try_map_with(|s: &str, e| {
+            s.parse()
+                .map(Token::Float)
+                .map_err(|err| Rich::custom(e.span(), format!("Unable to parse as 64-bit float: {}", err)))
+        })
         .boxed();
 
     let signed_int = one_of("+-")
         // .or_not()
         .then(digits)
         .to_slice()
-        .map(|s: &str| Token::Int(s.parse().unwrap()));
-    let unsigned_int = digits.to_slice().map(|s: &str| Token::UInt(s.parse().unwrap()));
+        .try_map_with(|s: &str, e| {
+            s.parse()
+                .map(Token::Int)
+                .map_err(|err| Rich::custom(e.span(), format!("Unable to parse as 64-bit signed int: {}", err)))
+        });
+    let unsigned_int = digits.to_slice().try_map_with(|s: &str, e| {
+        s.parse()
+            .map(Token::UInt)
+            .map_err(|err| Rich::custom(e.span(), format!("Unable to parse as 64-bit unsigned int: {}", err)))
+    });
 
     let number = choice((floating_number, signed_int, unsigned_int));
 
diff --git a/pyargus/tests/test_expr.py b/pyargus/tests/test_expr.py
index c53d33a..5f2780d 100644
--- a/pyargus/tests/test_expr.py
+++ b/pyargus/tests/test_expr.py
@@ -14,6 +14,8 @@ def test_correct_expr(data: st.DataObject) -> None:
     try:
         _ = argus.parse_expr(spec)
     except ValueError as e:
+        if "Unable to parse as 64-bit" in str(e):
+            return
         logging.critical(f"unable to parse expr: {spec}")
         raise e
     except BaseException as e: