diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 2288cb1c33a6..693475204896 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -870,6 +870,19 @@ void Parser::ParseAvailabilityAttribute(IdentifierInfo &Availability,
       break;
     }
 
+    // Special handling of 'NA' only when applied to introduced or
+    // deprecated.
+    if ((Keyword == Ident_introduced || Keyword == Ident_deprecated) &&
+        Tok.is(tok::identifier)) {
+      IdentifierInfo *NA = Tok.getIdentifierInfo();
+      if (NA->getName() == "NA") {
+        ConsumeToken();
+        if (Keyword == Ident_introduced)
+          UnavailableLoc = KeywordLoc;
+        continue;
+      }
+    }
+    
     SourceRange VersionRange;
     VersionTuple Version = ParseVersionTuple(VersionRange);
 
diff --git a/clang/test/SemaObjC/attr-availability-1.m b/clang/test/SemaObjC/attr-availability-1.m
index af0fcfe3537b..063407adaeee 100644
--- a/clang/test/SemaObjC/attr-availability-1.m
+++ b/clang/test/SemaObjC/attr-availability-1.m
@@ -95,3 +95,22 @@ id NSNibOwner, topNibObjects;
 - (void)Meth1 __attribute__((availability(macosx,introduced=10.3_0))); // expected-warning {{use same version number separators '_' or '.'}}
 - (void)Meth2 __attribute__((availability(macosx,introduced=10_3.1))); // expected-warning {{use same version number separators '_' or '.'}}
 @end
+
+// rdar://18804883
+@protocol P18804883
+- (void)proto_method __attribute__((availability(macosx,introduced=10_1,deprecated=NA))); // means nothing (not deprecated)
+@end
+
+@interface A18804883 <P18804883>
+- (void)interface_method __attribute__((availability(macosx,introduced=NA))); // expected-note {{'interface_method' has been explicitly marked unavailable here}}
+- (void)strange_method __attribute__((availability(macosx,introduced=NA,deprecated=NA)));  // expected-note {{'strange_method' has been explicitly marked unavailable here}}
+- (void) always_available __attribute__((availability(macosx,deprecated=NA)));
+@end
+
+void foo (A18804883* pa) {
+  [pa interface_method]; // expected-error {{'interface_method' is unavailable: not available on OS X}}
+  [pa proto_method];
+  [pa strange_method]; // expected-error {{'strange_method' is unavailable: not available on OS X}}
+  [pa always_available];
+}
+