diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index e4d91285b4458..2308a30cf754c 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -778,8 +778,6 @@ static bool ParseCASArgs(CASOptions &Opts, ArgList &Args,
   Opts.CacheSkipReplay |= Args.hasArg(OPT_cache_disable_replay);
   if (const Arg *A = Args.getLastArg(OPT_cas_path))
     Opts.CASOpts.CASPath = A->getValue();
-  else if (Opts.CASOpts.CASPath.empty())
-    Opts.CASOpts.CASPath = llvm::cas::getDefaultOnDiskCASPath();
 
   if (const Arg *A = Args.getLastArg(OPT_cas_plugin_path))
     Opts.CASOpts.PluginPath = A->getValue();
diff --git a/lib/Frontend/Frontend.cpp b/lib/Frontend/Frontend.cpp
index a21defd4be986..b5280fb575706 100644
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -466,6 +466,11 @@ bool CompilerInstance::setupCASIfNeeded(ArrayRef<const char *> Args) {
     return false;
 
   const auto &Opts = getInvocation().getCASOptions();
+  if (Opts.CASOpts.CASPath.empty() && Opts.CASOpts.PluginPath.empty()) {
+    Diagnostics.diagnose(SourceLoc(), diag::error_cas_initialization,
+                         "no CAS options provided");
+    return true;
+  }
   auto MaybeDB = Opts.CASOpts.getOrCreateDatabases();
   if (!MaybeDB) {
     Diagnostics.diagnose(SourceLoc(), diag::error_cas_initialization,
diff --git a/test/CAS/cas_output_backend.swift b/test/CAS/cas_output_backend.swift
index 992c4b6425f7c..0120ea00174be 100644
--- a/test/CAS/cas_output_backend.swift
+++ b/test/CAS/cas_output_backend.swift
@@ -13,6 +13,9 @@
 // RUN: echo "\"-disable-implicit-concurrency-module-import\"" >> %t/MyApp.cmd
 // RUN: echo "\"-parse-stdlib\"" >> %t/MyApp.cmd
 
+// RUN: not %target-swift-frontend -c -cache-compile-job %s -o %t/test.o @%t/MyApp.cmd 2>&1 | %FileCheck %s --check-prefix=NOT-CONFIG
+// NOT-CONFIG: error: CAS cannot be initialized from the specified '-cas-*' options: no CAS options provided
+
 // RUN: %target-swift-frontend -c -cache-compile-job -cas-path %t/cas %s -o %t/test.o @%t/MyApp.cmd
 // RUN: %cache-tool -cas-path %t/cas -cache-tool-action print-output-keys -- \
 // RUN:   %target-swift-frontend -c -cache-compile-job -cas-path %t/cas %s -o %t/test.o @%t/MyApp.cmd > %t/cache_key.json