diff --git a/clang/lib/Basic/TargetInfo.cpp b/clang/lib/Basic/TargetInfo.cpp
index 535c87ec1158e99170e210c86dc693efb2a480af..84cdaab5176fbd964fe6932cbd45f97bb5d2989a 100644
--- a/clang/lib/Basic/TargetInfo.cpp
+++ b/clang/lib/Basic/TargetInfo.cpp
@@ -548,11 +548,17 @@ bool TargetInfo::validateInputConstraint(ConstraintInfo *OutputConstraints,
     default:
       // Check if we have a matching constraint
       if (*Name >= '0' && *Name <= '9') {
-        unsigned i = *Name - '0';
+        const char *DigitStart = Name;
+        while (Name[1] >= '0' && Name[1] <= '9')
+          Name++;
+        const char *DigitEnd = Name;
+        unsigned i;
+        if (StringRef(DigitStart, DigitEnd - DigitStart + 1)
+                .getAsInteger(10, i))
+          return false;
 
         // Check if matching constraint is out of bounds.
-        if (i >= NumOutputs)
-          return false;
+        if (i >= NumOutputs) return false;
 
         // A number must refer to an output only operand.
         if (OutputConstraints[i].isReadWrite())
diff --git a/clang/test/Sema/asm.c b/clang/test/Sema/asm.c
index f386f520be4db00655f403dd32c99319a247c20a..41a8265600d6964472f3773fa0b4e28abcef3c63 100644
--- a/clang/test/Sema/asm.c
+++ b/clang/test/Sema/asm.c
@@ -197,3 +197,10 @@ void fn5() {
           : [g] "+r"(l)
           : "[g]"(l)); // expected-error {{invalid input constraint '[g]' in asm}}
 }
+
+void fn6() {
+    int a;
+  __asm__(""
+            : "=rm"(a), "=rm"(a)
+            : "11m"(a)) // expected-error {{invalid input constraint '11m' in asm}}
+}