diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 74c60bcdb62..300bd8fac0a 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -5995,7 +5995,9 @@ namespace ts {
             for (const memberType of types) {
                 for (const { escapedName } of getAugmentedPropertiesOfType(memberType)) {
                     if (!props.has(escapedName)) {
-                        props.set(escapedName, createUnionOrIntersectionProperty(unionType as UnionType, escapedName));
+                        const prop = createUnionOrIntersectionProperty(unionType as UnionType, escapedName);
+                        // May be undefined if the property is private
+                        if (prop) props.set(escapedName, prop);
                     }
                 }
             }
@@ -6177,7 +6179,7 @@ namespace ts {
                 t;
         }
 
-        function createUnionOrIntersectionProperty(containingType: UnionOrIntersectionType, name: __String): Symbol {
+        function createUnionOrIntersectionProperty(containingType: UnionOrIntersectionType, name: __String): Symbol | undefined {
             let props: Symbol[];
             const isUnion = containingType.flags & TypeFlags.Union;
             const excludeModifiers = isUnion ? ModifierFlags.NonPublicAccessibilityModifier : 0;
diff --git a/src/harness/externalCompileRunner.ts b/src/harness/externalCompileRunner.ts
index c829a6490bb..1f945cfcc9c 100644
--- a/src/harness/externalCompileRunner.ts
+++ b/src/harness/externalCompileRunner.ts
@@ -131,13 +131,13 @@ function removeExpectedErrors(errors: string, cwd: string): string {
 function isUnexpectedError(cwd: string) {
     return (error: string[]) => {
         ts.Debug.assertGreaterThanOrEqual(error.length, 1);
-        const match = error[0].match(/(.+\.ts)\((\d+),\d+\): error TS/);
+        const match = error[0].match(/(.+\.tsx?)\((\d+),\d+\): error TS/);
         if (!match) {
             return true;
         }
         const [, errorFile, lineNumberString] = match;
         const lines = fs.readFileSync(path.join(cwd, errorFile), { encoding: "utf8" }).split("\n");
-        const lineNumber = parseInt(lineNumberString);
+        const lineNumber = parseInt(lineNumberString) - 1;
         ts.Debug.assertGreaterThanOrEqual(lineNumber, 0);
         ts.Debug.assertLessThan(lineNumber, lines.length);
         const previousLine = lineNumber - 1 > 0 ? lines[lineNumber - 1] : "";
diff --git a/tests/cases/fourslash/completionsUnion.ts b/tests/cases/fourslash/completionsUnion.ts
index ed449936680..d9d1d3c792f 100644
--- a/tests/cases/fourslash/completionsUnion.ts
+++ b/tests/cases/fourslash/completionsUnion.ts
@@ -2,7 +2,9 @@
 
 ////interface I { x: number; }
 ////interface Many<T> extends ReadonlyArray<T> { extra: number; }
-////const x: I | I[] | Many<string> = { /**/ };
+////class C { private priv: number; }
+////const x: I | I[] | Many<string> | C = { /**/ };
 
 // We specifically filter out any array-like types.
+// Private members will be excluded by `createUnionOrIntersectionProperty`.
 verify.completionsAt("", ["x"]);