diff --git a/src/lib.rs b/src/lib.rs
index bf07dda..7d33a8e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -76,7 +76,7 @@ impl From<std::ops::RangeFull> for SpanRange {
 
 /// An input that can provide a span of a range of the input.
 pub trait Span<O> {
-    fn span(&self, idx: SpanRange) -> O;
+    fn span<R: Into<SpanRange>>(&self, idx: R) -> O;
 }
 
 /// The interface for types that can peek ahead to the next item.
@@ -169,8 +169,8 @@ impl<'a, T: Debug + 'a> Cursor for SliceCursor<'a, T> {
 }
 
 impl<'a, T: Debug + 'a> Span<&'a [T]> for SliceCursor<'a, T> {
-    fn span(&self, idx: SpanRange) -> &'a [T] {
-        match idx {
+    fn span<R: Into<SpanRange>>(&self, idx: R) -> &'a [T] {
+        match idx.into() {
             SpanRange::Range(r) => self.source.index(r),
             SpanRange::RangeTo(r) => self.source.index(r),
             SpanRange::RangeFrom(r) => self.source.index(r),
@@ -293,8 +293,8 @@ impl<'a> From<&'a str> for StrCursor<'a> {
 }
 
 impl<'a> Span<&'a str> for StrCursor<'a> {
-    fn span(&self, idx: SpanRange) -> &'a str {
-        match idx {
+    fn span<R: Into<SpanRange>>(&self, idx: R) -> &'a str {
+        match idx.into() {
             SpanRange::Range(r) => self.source.index(r),
             SpanRange::RangeTo(r) => self.source.index(r),
             SpanRange::RangeFrom(r) => self.source.index(r),