Index: test/Driver/unknown-arg.c
===================================================================
--- test/Driver/unknown-arg.c
+++ test/Driver/unknown-arg.c
@@ -12,6 +12,8 @@
 // RUN: FileCheck %s --check-prefix=CL-ERROR-DID-YOU-MEAN
 // RUN: %clang_cl -cake-is-lie -%0 -%d -HHHH -munknown-to-clang-option -print-stats -funknown-to-clang-option -c -Wno-unknown-argument -### -- %s 2>&1 | \
 // RUN: FileCheck %s --check-prefix=SILENT
+// RUN: not %clang -cc1asphalt -help 2>&1 | \
+// RUN: FileCheck %s --check-prefix=UNKNOWN-INTEGRATED
 
 // CHECK: error: unknown argument: '-cake-is-lie'
 // CHECK: error: unknown argument: '-%0'
@@ -41,6 +43,7 @@
 // CL-ERROR-DID-YOU-MEAN: error: unknown argument ignored in clang-cl '-helo' (did you mean '-help'?)
 // SILENT-NOT: error:
 // SILENT-NOT: warning:
+// UNKNOWN-INTEGRATED: error: unknown integrated tool 'asphalt'. Valid tools include '-cc1' and '-cc1as'.
 
 
 // RUN: %clang -S %s -o %t.s  -Wunknown-to-clang-option 2>&1 | FileCheck --check-prefix=IGNORED %s
Index: tools/driver/driver.cpp
===================================================================
--- tools/driver/driver.cpp
+++ tools/driver/driver.cpp
@@ -311,7 +311,8 @@
     return cc1as_main(argv.slice(2), argv[0], GetExecutablePathVP);
 
   // Reject unknown tools.
-  llvm::errs() << "error: unknown integrated tool '" << Tool << "'\n";
+  llvm::errs() << "error: unknown integrated tool '" << Tool << "'. "
+               << "Valid tools include '-cc1' and '-cc1as'.\n";
   return 1;
 }