diff --git a/src/core/link-to-dfn.js b/src/core/link-to-dfn.js
index 508de12445..e70e0fed14 100644
--- a/src/core/link-to-dfn.js
+++ b/src/core/link-to-dfn.js
@@ -57,7 +57,8 @@ export function run(conf, doc, cb) {
         if (dfn[0].dataset.cite) {
           $ant[0].dataset.cite = dfn[0].dataset.cite;
         } else {
-          $ant.attr("href", "#" + dfn.prop("id")).addClass("internalDFN");
+          const frag = "#" + encodeURIComponent(dfn.prop("id"));
+          $ant.attr("href", frag).addClass("internalDFN");
         }
         // add a bikeshed style indication of the type of link
         if (!$ant.attr("data-link-type")) {