1 files changed, 10 insertions, 7 deletions
diff --git a/src/client/util/ProsemirrorExampleTransfer.ts b/src/client/util/ProsemirrorExampleTransfer.ts
index da3815181..81cf54d4c 100644
--- a/src/client/util/ProsemirrorExampleTransfer.ts
+++ b/src/client/util/ProsemirrorExampleTransfer.ts
@@ -175,13 +175,16 @@ export default function buildKeymap<S extends Schema<any>>(schema: S, mapKeys?:
         });
         const path = (state.doc.resolve(state.selection.from - 1) as any).path;
         const spaceSeparator = path[path.length - 3].childCount > 1 ? 0 : -1;
-        const textsel = TextSelection.create(state.doc, range!.end - path[path.length - 3].lastChild.nodeSize + spaceSeparator, range!.end);
-        const text = range ? state.doc.textBetween(textsel.from, textsel.to) : "";
-        let whitespace = text.length - 1;
-        for (; whitespace >= 0 && text[whitespace] !== " "; whitespace--) { }
-        if (text.endsWith(":")) {
-            dispatch(state.tr.addMark(textsel.from + whitespace + 1, textsel.to, schema.marks.metadata.create() as any).
-                addMark(textsel.from + whitespace + 1, textsel.to - 2, schema.marks.metadataKey.create() as any));
+        const anchor = range!.end - path[path.length - 3].lastChild.nodeSize + spaceSeparator;
+        if (anchor >= 0) {
+            const textsel = TextSelection.create(state.doc, anchor, range!.end);
+            const text = range ? state.doc.textBetween(textsel.from, textsel.to) : "";
+            let whitespace = text.length - 1;
+            for (; whitespace >= 0 && text[whitespace] !== " "; whitespace--) { }
+            if (text.endsWith(":")) {
+                dispatch(state.tr.addMark(textsel.from + whitespace + 1, textsel.to, schema.marks.metadata.create() as any).
+                    addMark(textsel.from + whitespace + 1, textsel.to - 2, schema.marks.metadataKey.create() as any));
+            }
         }
         return false;
     });