diff --git a/clang/test/Sema/inline-asm-validate.c b/clang/test/Sema/inline-asm-validate.c
--- a/clang/test/Sema/inline-asm-validate.c
+++ b/clang/test/Sema/inline-asm-validate.c
@@ -7,4 +7,8 @@
   // Ensure we accept pointer and non-pointer arguments to "p" constrained
   // inputs.
   asm (""::"p"(t), "p"(p), "p"(&t));
+  // TODO: Ensure we accept p output constraints.
+  asm ("":"=p"(t)); // expected-error{{invalid output constraint '=p' in asm}}
+  asm ("":"=p"(p)); // expected-error{{invalid output constraint '=p' in asm}}
+  asm ("":"=p"(&t)); // expected-error{{invalid output constraint '=p' in asm}}
 }