diff --git a/clang/lib/Sema/SemaFeatureAvailability.cpp b/clang/lib/Sema/SemaFeatureAvailability.cpp
index 781fc9e8e2ff4..e5319941a99a7 100644
--- a/clang/lib/Sema/SemaFeatureAvailability.cpp
+++ b/clang/lib/Sema/SemaFeatureAvailability.cpp
@@ -33,10 +33,18 @@ static bool isFeatureUseGuarded(const DomainAvailabilityAttr *AA,
 static void diagnoseDeclFeatureAvailability(const NamedDecl *D,
                                             SourceLocation Loc,
                                             Decl *ContextDecl, Sema &S) {
-  for (auto *Attr : D->specific_attrs<DomainAvailabilityAttr>())
+  for (auto *Attr : D->specific_attrs<DomainAvailabilityAttr>()) {
+    std::string FeatureUse = Attr->getDomain().str();
+    // Skip checking if the feature is always enabled.
+    if (!Attr->getUnavailable() &&
+        S.Context.getFeatureAvailInfo(FeatureUse).Kind ==
+            FeatureAvailKind::AlwaysAvailable)
+      continue;
+
     if (!isFeatureUseGuarded(Attr, ContextDecl, S.Context))
       S.Diag(Loc, diag::err_unguarded_feature)
-          << D << Attr->getDomain().str() << Attr->getUnavailable();
+          << D << FeatureUse << Attr->getUnavailable();
+  }
 }
 
 class DiagnoseUnguardedFeatureAvailability
@@ -165,6 +173,12 @@ void DiagnoseUnguardedFeatureAvailability::diagnoseDeclFeatureAvailability(
     const NamedDecl *D, SourceLocation Loc) {
   for (auto *Attr : D->specific_attrs<DomainAvailabilityAttr>()) {
     std::string FeatureUse = Attr->getDomain().str();
+    // Skip checking if the feature is always enabled.
+    if (!Attr->getUnavailable() &&
+        SemaRef.Context.getFeatureAvailInfo(FeatureUse).Kind ==
+            FeatureAvailKind::AlwaysAvailable)
+      continue;
+
     if (!isFeatureUseGuarded(Attr))
       SemaRef.Diag(Loc, diag::err_unguarded_feature)
           << D << FeatureUse << Attr->getUnavailable();
diff --git a/clang/test/CodeGen/feature-availability.c b/clang/test/CodeGen/feature-availability.c
index 94a72e4f67e34..2956a61b5160f 100644
--- a/clang/test/CodeGen/feature-availability.c
+++ b/clang/test/CodeGen/feature-availability.c
@@ -1,11 +1,14 @@
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -ffeature-availability=feature1:on -ffeature-availability=feature2:off -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-llvm -o - -DUSE_DOMAIN %s | FileCheck --check-prefixes=CHECK,DOMAIN %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-llvm -o - -DUSE_DOMAIN -DALWAYS_ENABLED %s | FileCheck --check-prefixes=CHECK,DOMAIN %s
 
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -ffeature-availability=feature1:on -ffeature-availability=feature2:off -emit-pch -o %t %s
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -ffeature-availability=feature1:on -ffeature-availability=feature2:off -include-pch %t -emit-llvm -o - %s | FileCheck %s
 
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-pch -o %t -DUSE_DOMAIN %s
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -include-pch %t -emit-llvm -o - -DUSE_DOMAIN %s | FileCheck --check-prefixes=CHECK,DOMAIN %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-pch -o %t -DUSE_DOMAIN -DALWAYS_ENABLED %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -include-pch %t -emit-llvm -o - -DUSE_DOMAIN -DALWAYS_ENABLED %s | FileCheck --check-prefixes=CHECK,DOMAIN %s
 
 // CHECK: %[[STRUCT_S0:.*]] = type { i32 }
 // CHECK: @g0 = external global i32, align 4
@@ -22,7 +25,11 @@
 #ifdef USE_DOMAIN
 // DOMAIN: @g3 = extern_weak global i32, align 4
 
+#ifdef ALWAYS_ENABLED
+CLANG_ALWAYS_ENABLED_AVAILABILITY_DOMAIN(feature1);
+#else
 CLANG_ENABLED_AVAILABILITY_DOMAIN(feature1);
+#endif
 CLANG_DISABLED_AVAILABILITY_DOMAIN(feature2);
 #endif
 
diff --git a/clang/test/CodeGenObjC/feature-availability.m b/clang/test/CodeGenObjC/feature-availability.m
index 67ad95dcf260f..13b2a43b9d756 100644
--- a/clang/test/CodeGenObjC/feature-availability.m
+++ b/clang/test/CodeGenObjC/feature-availability.m
@@ -1,15 +1,21 @@
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -ffeature-availability=feature1:on -ffeature-availability=feature2:off -ffeature-availability=feature3:on -emit-llvm -o - %s | FileCheck %s
 // RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-llvm -o - -DUSE_DOMAIN %s | FileCheck %s
+// RUN: %clang_cc1 -triple arm64-apple-macosx -fblocks -emit-llvm -o - -DUSE_DOMAIN -DALWAYS_ENABLED %s | FileCheck %s
 
 #include <availability_domain.h>
 
 #define AVAIL 0
 
 #ifdef USE_DOMAIN
+#ifdef ALWAYS_ENABLED
+CLANG_ALWAYS_ENABLED_AVAILABILITY_DOMAIN(feature1);
+CLANG_ALWAYS_ENABLED_AVAILABILITY_DOMAIN(feature3);
+#else
 CLANG_ENABLED_AVAILABILITY_DOMAIN(feature1);
-CLANG_DISABLED_AVAILABILITY_DOMAIN(feature2);
 CLANG_ENABLED_AVAILABILITY_DOMAIN(feature3);
 #endif
+CLANG_DISABLED_AVAILABILITY_DOMAIN(feature2);
+#endif
 
 // CHECK: @"OBJC_CLASS_$_C0" = global %struct._class_t { ptr @"OBJC_METACLASS_$_C0", ptr null, ptr @_objc_empty_cache, ptr @_objc_empty_vtable, ptr @"_OBJC_CLASS_RO_$_C0" }, section "__DATA, __objc_data", align 8
 // CHECK-NEXT: @"OBJC_METACLASS_$_C0" = global %struct._class_t { ptr @"OBJC_METACLASS_$_C0", ptr @"OBJC_CLASS_$_C0", ptr @_objc_empty_cache, ptr @_objc_empty_vtable, ptr @"_OBJC_METACLASS_RO_$_C0" }, section "__DATA, __objc_data", align 8
diff --git a/clang/test/Sema/feature-availability.c b/clang/test/Sema/feature-availability.c
index 9b2def0eb3760..dbc35cb9e3c48 100644
--- a/clang/test/Sema/feature-availability.c
+++ b/clang/test/Sema/feature-availability.c
@@ -258,15 +258,14 @@ void test7(void) {
 
 #ifdef USE_DOMAIN
 void test8(void) {
-  // FIXME: Use of 'func21()' should not be diagnosed because feature5 is always available.
-  func21(); // expected-error {{cannot use 'func21' because feature 'feature5' is unavailable in this context}}
+  func21();
   func22(); // expected-error {{cannot use 'func22' because feature 'feature5' is available in this context}}
 
   if (__builtin_available(domain:feature5)) {
     func21();
     func22(); // expected-error {{cannot use 'func22' because feature 'feature5' is available in this context}}
   } else {
-    func21(); // expected-error {{cannot use 'func21' because feature 'feature5' is unavailable in this context}}
+    func21();
     func22();
   }
 }
diff --git a/clang/test/SemaObjC/feature-availability.m b/clang/test/SemaObjC/feature-availability.m
index c14a8df04e008..d2c9195ca3813 100644
--- a/clang/test/SemaObjC/feature-availability.m
+++ b/clang/test/SemaObjC/feature-availability.m
@@ -1,5 +1,6 @@
-// RUN: %clang_cc1 -fblocks -ffeature-availability=feature1:ON -ffeature-availability=feature2:OFF -fsyntax-only -verify %s
-// RUN: %clang_cc1 -fblocks -fsyntax-only -verify -DUSE_DOMAIN %s
+// RUN: %clang_cc1 -fblocks -ffeature-availability=feature1:ON -ffeature-availability=feature2:OFF -fsyntax-only -verify=expected,enabled %s
+// RUN: %clang_cc1 -fblocks -fsyntax-only -verify=expected,enabled -DUSE_DOMAIN %s
+// RUN: %clang_cc1 -fblocks -fsyntax-only -verify=expected -DUSE_DOMAIN -DALWAYS_ENABLED %s
 
 #include <availability_domain.h>
 
@@ -7,7 +8,11 @@
 #define UNAVAIL 1
 
 #ifdef USE_DOMAIN
+#ifdef ALWAYS_ENABLED
+CLANG_ALWAYS_ENABLED_AVAILABILITY_DOMAIN(feature1);
+#else
 CLANG_ENABLED_AVAILABILITY_DOMAIN(feature1);
+#endif
 CLANG_DISABLED_AVAILABILITY_DOMAIN(feature2);
 #endif
 
@@ -19,18 +24,18 @@
 
 @interface C0 {
   struct S0 ivar0; // expected-error {{cannot use 'S0' because feature 'feature1' is available in this context}}
-  struct S1 ivar1; // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+  struct S1 ivar1; // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
   struct S1 ivar2 __attribute__((availability(domain:feature1, AVAIL)));
-  struct S1 ivar3 __attribute__((availability(domain:feature1, UNAVAIL))); // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+  struct S1 ivar3 __attribute__((availability(domain:feature1, UNAVAIL))); // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 }
 @property struct S0 prop0; // expected-error {{cannot use 'S0' because feature 'feature1' is available in this context}}
-@property struct S1 prop1; // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+@property struct S1 prop1; // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 @property struct S1 prop2 __attribute__((availability(domain:feature1, AVAIL)));
-@property struct S1 prop3 __attribute__((availability(domain:feature1, UNAVAIL))); // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+@property struct S1 prop3 __attribute__((availability(domain:feature1, UNAVAIL))); // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 -(struct S0)m0; // expected-error {{cannot use 'S0' because feature 'feature1' is available in this context}}
--(struct S1)m1; // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+-(struct S1)m1; // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 -(struct S1)m2 __attribute__((availability(domain:feature1, AVAIL)));
--(struct S1)m3 __attribute__((availability(domain:feature1, UNAVAIL))); // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+-(struct S1)m3 __attribute__((availability(domain:feature1, UNAVAIL))); // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 @end
 
 @class Base0;
@@ -59,7 +64,7 @@ @interface NSObject
 @interface Base7<T> : NSObject
 @end
 
-@interface Derived3 : Base7<Base0 *> // expected-error {{cannot use 'Base0' because feature 'feature1' is unavailable in this context}}
+@interface Derived3 : Base7<Base0 *> // enabled-error {{cannot use 'Base0' because feature 'feature1' is unavailable in this context}}
 @end
 
 __attribute__((availability(domain:feature1, AVAIL))) // expected-note {{is incompatible with __attribute__((availability(domain:feature1, 0)))}} expected-note 2 {{feature attribute __attribute__((availability(domain:feature1, 0)))}}
@@ -116,7 +121,7 @@ @interface Derived1(C1) // expected-error {{cannot merge incompatible feature at
 @end
 
 @protocol P0
-@property struct S1 *p0; // expected-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
+@property struct S1 *p0; // enabled-error {{cannot use 'S1' because feature 'feature1' is unavailable in this context}}
 @end
 
 __attribute__((availability(domain:feature1, AVAIL)))
@@ -198,8 +203,8 @@ @implementation Derived9 : Base9
 -(void)m4 {
   // Check that this method doesn't inherit the domain availablity attribute
   // from the base class method.
-  func1(); // expected-error {{cannot use 'func1' because feature 'feature1' is unavailable in this context}}
+  func1(); // enabled-error {{cannot use 'func1' because feature 'feature1' is unavailable in this context}}
 
-  [super m4]; // expected-error {{cannot use 'm4' because feature 'feature1' is unavailable in this context}}
+  [super m4]; // enabled-error {{cannot use 'm4' because feature 'feature1' is unavailable in this context}}
 }
 @end