diff --git a/src/runs/execution/tools/wikipedia-tool.ts b/src/runs/execution/tools/wikipedia-tool.ts
index b9862dd..6e3a70c 100644
--- a/src/runs/execution/tools/wikipedia-tool.ts
+++ b/src/runs/execution/tools/wikipedia-tool.ts
@@ -79,7 +79,7 @@ export function wikipediaTool(
       query: input.question,
       documents: output.results.flatMap((document, idx) =>
         Array.from(
-          splitString(document.fields.markdown as string, {
+          splitString((document.fields.markdown as string | null) || '', {
             size: passageSizeTokens * CHARS_PER_TOKEN_AVG,
             overlap: overlapTokens * CHARS_PER_TOKEN_AVG
           })