commit - 921165feb60b35f5fff3c8ca30107a3fb5273c46
commit + caf5a2e4344d368c834c8d00be84873248d843bc
blob - 14c752717f17798ba89ae5070c6cc6291d9f41c8
blob + 486f07c6fa14e952d651a804ec4d8c6ab195da37
--- src/parser.rs
+++ src/parser.rs
@@ -166,7 +166,10 @@ fn time_unit(i: &str) -> IResult<&str, TimeUnit> {
 
 fn time_amount(i: &str) -> IResult<&str, TimeAmount> {
     map(
-        tuple((map_res(digit1, str::parse::<usize>), time_unit)),
+        tuple((
+            verify(map_res(digit1, str::parse::<usize>), |d: &usize| *d > 0),
+            time_unit,
+        )),
         |(amount, unit)| TimeAmount::new(amount, unit),
     )(i)
 }