diff --git a/test/MC/ARM/thumb-diagnostics.s b/test/MC/ARM/thumb-diagnostics.s
new file mode 100644
index 00000000000..c8528c58564
--- /dev/null
+++ b/test/MC/ARM/thumb-diagnostics.s
@@ -0,0 +1,10 @@
+@ RUN: not llvm-mc -triple=thumbv6-apple-darwin < %s 2> %t
+@ RUN: FileCheck --check-prefix=CHECK-ERRORS < %t %s
+
+@ Check for various assembly diagnostic messages on invalid input.
+
+@ ADD instruction w/o 'S' suffix.
+        add r1, r2, r3
+@ CHECK-ERRORS: error: invalid instruction
+@ CHECK-ERRORS:         add r1, r2, r3
+@ CHECK-ERRORS:         ^