diff --git a/src/compiler/commandLineParser.ts b/src/compiler/commandLineParser.ts
index c56a18b3ab2..c9df1747999 100644
--- a/src/compiler/commandLineParser.ts
+++ b/src/compiler/commandLineParser.ts
@@ -326,9 +326,12 @@ namespace ts {
                                 if (hasProperty(map, key)) {
                                     options[opt.name] = map[key];
                                 }
-                                else {
+                                else if (opt.error) {
                                     errors.push(createCompilerDiagnostic(opt.error));
                                 }
+                                else {
+                                    Debug.fail(`Command line option for '${opt.name}' doesn't account for invalid options.`);
+                                }
                         }
                     }
                     else {