Index: clang/include/clang/Basic/Features.def
===================================================================
--- clang/include/clang/Basic/Features.def
+++ clang/include/clang/Basic/Features.def
@@ -118,6 +118,8 @@
 FEATURE(objc_generics, LangOpts.ObjC)
 FEATURE(objc_generics_variance, LangOpts.ObjC)
 FEATURE(objc_class_property, LangOpts.ObjC)
+FEATURE(objc_c_static_assert, true)
+FEATURE(objc_cxx_static_assert, LangOpts.CPlusPlus11)
 // C11 features
 FEATURE(c_alignas, LangOpts.C11)
 FEATURE(c_alignof, LangOpts.C11)
Index: clang/lib/Parse/ParseDecl.cpp
===================================================================
--- clang/lib/Parse/ParseDecl.cpp
+++ clang/lib/Parse/ParseDecl.cpp
@@ -3889,6 +3889,9 @@
 /// ParseStructDeclaration - Parse a struct declaration without the terminating
 /// semicolon.
 ///
+/// Note that a struct declaration refers to a declaration in a struct,
+/// not to the declaration of a struct.
+///
 ///       struct-declaration:
 /// [C2x]   attributes-specifier-seq[opt]
 ///           specifier-qualifier-list struct-declarator-list
Index: clang/lib/Parse/ParseObjc.cpp
===================================================================
--- clang/lib/Parse/ParseObjc.cpp
+++ clang/lib/Parse/ParseObjc.cpp
@@ -623,6 +623,8 @@
     }
     // Ignore excess semicolons.
     if (Tok.is(tok::semi)) {
+      // FIXME: This should use ConsumeExtraSemi() for extraneous semicolons,
+      // to make -Wextra-semi diagnose them.
       ConsumeToken();
       continue;
     }
@@ -646,7 +648,19 @@
       // erroneous r_brace would cause an infinite loop if not handled here.
       if (Tok.is(tok::r_brace))
         break;
+
       ParsedAttributesWithRange attrs(AttrFactory);
+
+      // Since we call ParseDeclarationOrFunctionDefinition() instead of
+      // ParseExternalDeclaration() below (so that this doesn't parse nested
+      // @interfaces), this needs to duplicate some code from the latter.
+      if (Tok.isOneOf(tok::kw_static_assert, tok::kw__Static_assert)) {
+        SourceLocation DeclEnd;
+        allTUVariables.push_back(
+            ParseDeclaration(DeclaratorContext::FileContext, DeclEnd, attrs));
+        continue;
+      }
+
       allTUVariables.push_back(ParseDeclarationOrFunctionDefinition(attrs));
       continue;
     }
@@ -1875,6 +1889,7 @@
 ///     ';'
 ///     objc-instance-variable-decl-list objc-visibility-spec
 ///     objc-instance-variable-decl-list objc-instance-variable-decl ';'
+///     objc-instance-variable-decl-list static_assert-declaration
 ///     objc-instance-variable-decl-list ';'
 ///
 ///   objc-visibility-spec:
@@ -1945,6 +1960,15 @@
       return cutOffParsing();
     }
 
+    // This needs to duplicate a small amount of code from
+    // ParseStructUnionBody() for things that should work in both
+    // C struct and in Objective-C class instance variables.
+    if (Tok.isOneOf(tok::kw_static_assert, tok::kw__Static_assert)) {
+      SourceLocation DeclEnd;
+      ParseStaticAssertDeclaration(DeclEnd);
+      continue;
+    }
+
     auto ObjCIvarCallback = [&](ParsingFieldDeclarator &FD) {
       Actions.ActOnObjCContainerStartDefinition(interfaceDecl);
       // Install the declarator into the interface decl.
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -2998,7 +2998,6 @@
 
     // These shouldn't make it here.
     case Decl::ObjCAtDefsField:
-    case Decl::ObjCIvar:
       llvm_unreachable("forming non-member reference to ivar?");
 
     // Enum constants are always r-values and never references.
@@ -3016,6 +3015,7 @@
     // exist in the high-level semantics.
     case Decl::Field:
     case Decl::IndirectField:
+    case Decl::ObjCIvar:
       assert(getLangOpts().CPlusPlus &&
              "building reference to field in C?");
 
Index: clang/test/Parser/objc-static-assert.m
===================================================================
--- /dev/null
+++ clang/test/Parser/objc-static-assert.m
@@ -0,0 +1,23 @@
+// RUN: %clang_cc1 -fobjc-runtime=macosx-fragile -fsyntax-only -verify -Wno-objc-root-class %s
+// RUN: %clang_cc1 -std=c89 -fobjc-runtime=macosx-fragile -fsyntax-only -verify -Wno-objc-root-class %s
+
+#if !__has_feature(objc_c_static_assert)
+#error failed
+#endif
+
+@interface A {
+  int a;
+  _Static_assert(1, "");
+  _Static_assert(0, ""); // expected-error {{static_assert failed}}
+
+  _Static_assert(a, ""); // expected-error {{use of undeclared identifier 'a'}}
+  _Static_assert(sizeof(a), ""); // expected-error {{use of undeclared identifier 'a'}}
+}
+
+_Static_assert(1, "");
+
+@end
+
+struct S {
+  @defs(A);
+};
Index: clang/test/Parser/objc-static-assert.mm
===================================================================
--- /dev/null
+++ clang/test/Parser/objc-static-assert.mm
@@ -0,0 +1,74 @@
+// RUN: %clang_cc1 -fsyntax-only -verify -Wno-objc-root-class %s
+// RUN: %clang_cc1 -std=c++98 -fsyntax-only -verify -Wno-objc-root-class %s
+
+#if !__has_feature(objc_c_static_assert)
+#error failed
+#endif
+
+#if __cplusplus >= 201103L
+
+#if !__has_feature(objc_cxx_static_assert)
+#error failed
+#endif
+
+// C++11
+
+@interface A {
+  int a;
+  static_assert(1, "");
+  _Static_assert(1, "");
+
+  static_assert(0, ""); // expected-error {{static_assert failed}}
+  _Static_assert(0, ""); // expected-error {{static_assert failed}}
+
+  static_assert(a, ""); // expected-error {{static_assert expression is not an integral constant expression}}
+  static_assert(sizeof(a) == 4, "");
+  static_assert(sizeof(a) == 3, ""); // expected-error {{static_assert failed}}
+}
+
+static_assert(1, "");
+_Static_assert(1, "");
+
+- (void)f;
+@end
+
+@implementation A {
+  int b;
+  static_assert(1, "");
+  _Static_assert(1, "");
+  static_assert(sizeof(b) == 4, "");
+  static_assert(sizeof(b) == 3, ""); // expected-error {{static_assert failed}}
+}
+
+static_assert(1, "");
+
+- (void)f {
+  static_assert(1, "");
+}
+@end
+
+@interface B
+@end
+
+@interface B () {
+  int b;
+  static_assert(sizeof(b) == 4, "");
+  static_assert(sizeof(b) == 3, ""); // expected-error {{static_assert failed}}
+}
+@end
+
+#else
+
+#if __has_feature(objc_cxx_static_assert)
+#error failed
+#endif
+
+// C++98
+@interface A {
+  int a;
+  static_assert(1, ""); // expected-error {{type name requires a specifier or qualifier}} expected-error{{expected parameter declarator}} expected-error {{expected ')'}} expected-note {{to match this '('}}
+  _Static_assert(1, "");
+  _Static_assert(0, ""); // expected-error {{static_assert failed}}
+}
+@end
+#endif