diff --git a/src/services/codefixes/convertToAsyncFunction.ts b/src/services/codefixes/convertToAsyncFunction.ts
index b9b5fe150d5..5625f5b4a55 100644
--- a/src/services/codefixes/convertToAsyncFunction.ts
+++ b/src/services/codefixes/convertToAsyncFunction.ts
@@ -172,9 +172,9 @@ namespace ts.codefix {
 
                 // if the identifier refers to a function we want to add the new synthesized variable for the declaration (ex. blob in let blob = res(arg))
                 // Note - the choice of the last call signature is arbitrary
-                if (lastCallSignature && lastCallSignature.parameters.length && !synthNamesMap.has(symbolIdString)) {
-                    const firstParameter = lastCallSignature.parameters[0];
-                    const ident = isParameter(firstParameter.valueDeclaration) && tryCast(firstParameter.valueDeclaration.name, isIdentifier) || createOptimisticUniqueName("result");
+                if (lastCallSignature && !synthNamesMap.has(symbolIdString)) {
+                    const firstParameter = firstOrUndefined(lastCallSignature.parameters);
+                    const ident = firstParameter && isParameter(firstParameter.valueDeclaration) && tryCast(firstParameter.valueDeclaration.name, isIdentifier) || createOptimisticUniqueName("result");
                     const synthName = getNewNameIfConflict(ident, collidingSymbolMap);
                     synthNamesMap.set(symbolIdString, synthName);
                     allVarNames.push({ identifier: synthName.identifier, symbol });