diff --git a/src/formatting.rs b/src/formatting.rs
index bea3a6c..6a4640b 100644
--- a/src/formatting.rs
+++ b/src/formatting.rs
@@ -32,16 +32,10 @@ pub fn pretty_eval(input: &str, max_digits: usize) -> Result<String, Error> {
 }
 
 trait StrExt {
-    fn rsplit_once_last<'a>(
-        &'a self,
-        delimiters: &[&'static str],
-    ) -> (&'a str, &'static str, &'a str);
+    fn rsplit_once_last<'a, 'b>(&'a self, delimiters: &[&'b str]) -> (&'a str, &'b str, &'a str);
 }
 impl StrExt for str {
-    fn rsplit_once_last<'a>(
-        &'a self,
-        delimiters: &[&'static str],
-    ) -> (&'a str, &'static str, &'a str) {
+    fn rsplit_once_last<'a, 'b>(&'a self, delimiters: &[&'b str]) -> (&'a str, &'b str, &'a str) {
         delimiters
             .iter()
             .filter_map(|delimiter| self.rfind(delimiter).map(|i| (delimiter, i)))