diff --git a/lib/Basic/TargetInfo.cpp b/lib/Basic/TargetInfo.cpp
index 70ea235..699f7d4 100644
--- a/lib/Basic/TargetInfo.cpp
+++ b/lib/Basic/TargetInfo.cpp
@@ -373,7 +373,7 @@
     Name++;
   }
 
-  return true;
+  return Info.allowsMemory() || Info.allowsRegister();
 }
 
 bool TargetInfo::resolveSymbolicName(const char *&Name,
diff --git a/test/Sema/asm.c b/test/Sema/asm.c
index 2c60085..c81f16a 100644
--- a/test/Sema/asm.c
+++ b/test/Sema/asm.c
@@ -130,3 +130,19 @@
   __asm("": : "a"(*s)); // expected-error {{dereference of pointer to incomplete type 'struct S'}}
   __asm("": "=a" (*s) :); // expected-error {{dereference of pointer to incomplete type 'struct S'}}
 }
+
+// PR15759.
+double test15() {
+  double ret = 0;
+  __asm("0.0":"="(ret)); // expected-error {{invalid output constraint '=' in asm}}
+  __asm("0.0":"=&"(ret)); // expected-error {{invalid output constraint '=&' in asm}}
+  __asm("0.0":"+?"(ret)); // expected-error {{invalid output constraint '+?' in asm}}
+  __asm("0.0":"+!"(ret)); // expected-error {{invalid output constraint '+!' in asm}}
+  __asm("0.0":"+#"(ret)); // expected-error {{invalid output constraint '+#' in asm}}
+  __asm("0.0":"+*"(ret)); // expected-error {{invalid output constraint '+*' in asm}}
+  __asm("0.0":"=%"(ret)); // expected-error {{invalid output constraint '=%' in asm}}
+  __asm("0.0":"=,="(ret)); // expected-error {{invalid output constraint '=,=' in asm}}
+  __asm("0.0":"=,g"(ret)); // no-error
+  __asm("0.0":"=g"(ret)); // no-error
+  return ret;
+}