diff --git a/src/services/documentRegistry.ts b/src/services/documentRegistry.ts
index ee99aed930c4e..7a21cebb4f37f 100644
--- a/src/services/documentRegistry.ts
+++ b/src/services/documentRegistry.ts
@@ -184,7 +184,7 @@ namespace ts {
 
             const bucket = getBucketForCompilationSettings(key, /*createIfMissing*/ true);
             let entry = bucket.get(path);
-            const scriptTarget = scriptKind === ScriptKind.JSON ? ScriptTarget.JSON : compilationSettings.target;
+            const scriptTarget = scriptKind === ScriptKind.JSON ? ScriptTarget.JSON : compilationSettings.target || ScriptTarget.ES5;
             if (!entry && externalCache) {
                 const sourceFile = externalCache.getDocument(key, path);
                 if (sourceFile) {
@@ -199,7 +199,7 @@ namespace ts {
 
             if (!entry) {
                 // Have never seen this file with these settings.  Create a new source file for it.
-                const sourceFile = createLanguageServiceSourceFile(fileName, scriptSnapshot, scriptTarget!, version, /*setNodeParents*/ false, scriptKind); // TODO: GH#18217
+                const sourceFile = createLanguageServiceSourceFile(fileName, scriptSnapshot, scriptTarget, version, /*setNodeParents*/ false, scriptKind);
                 if (externalCache) {
                     externalCache.setDocument(key, path, sourceFile);
                 }