diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 3162b7cde239..15b8c83d1b36 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -491,6 +491,7 @@ bool TargetInfo::validateOutputConstraint(ConstraintInfo &Info) const {
         Name++;
       if (Name[1] != ',')
         return false;
+      break;
     case '?': // Disparage slightly code.
     case '!': // Disparage severely.
     case '*': // Ignore for choosing register preferences.
@@ -623,9 +624,14 @@ bool TargetInfo::validateInputConstraint(ConstraintInfo *OutputConstraints,
       break;
     case ',': // multiple alternative constraint.  Ignore comma.
       break;
+    case '#': // Ignore as constraint.
+      while (Name[1] && Name[1] != ',')
+        Name++;
+      if (Name[1] != ',')
+        return false;
+      break;
     case '?': // Disparage slightly code.
     case '!': // Disparage severely.
-    case '#': // Ignore as constraint.
     case '*': // Ignore for choosing register preferences.
       break;  // Pass them.
     }
diff --git a/clang/test/Sema/asm.c b/clang/test/Sema/asm.c
index b4000cb5ff89..10d845e3d0bb 100644
--- a/clang/test/Sema/asm.c
+++ b/clang/test/Sema/asm.c
@@ -183,3 +183,10 @@ void fn3() {
  __asm__(""
           : "+#r"(l)); // expected-error {{invalid output constraint '+#r' in asm}}
 }
+
+void fn4() {
+  int l;
+ __asm__(""
+          : "=r"(l)
+          : "#m"(l)); // expected-error {{invalid input constraint '#m' in asm}}
+}