diff --git a/src/protocol/input_source.rs b/src/protocol/input_source.rs
index 4940c2b17a6a2fe4468461bb360a8746ee671451..f2cf10693ae87bc134610829d91344bcc1f221f1 100644
--- a/src/protocol/input_source.rs
+++ b/src/protocol/input_source.rs
@@ -24,7 +24,7 @@ impl InputSpan {
     // This must only be used if you're sure that the span will not be involved
     // in creating an error message.
     #[inline]
-    pub fn new() -> InputSpan {
+    pub const fn new() -> InputSpan {
         InputSpan{ begin: InputPosition{ line: 0, offset: 0 }, end: InputPosition{ line: 0, offset: 0 }}
     }