diff --git a/lib/ClangImporter/SwiftDeclSynthesizer.cpp b/lib/ClangImporter/SwiftDeclSynthesizer.cpp
index 40ed851c99a31..19b774af92d83 100644
--- a/lib/ClangImporter/SwiftDeclSynthesizer.cpp
+++ b/lib/ClangImporter/SwiftDeclSynthesizer.cpp
@@ -3183,7 +3183,7 @@ FuncDecl *SwiftDeclSynthesizer::makeAvailabilityDomainPredicate(
       BuiltinIntegerType::get(1, ctx), ImporterImpl.ImportedHeaderUnit);
   funcDecl->setBodySynthesizer(synthesizeAvailabilityDomainPredicateBody,
                                (void *)var);
-  funcDecl->setAccess(AccessLevel::Internal);
+  funcDecl->setAccess(AccessLevel::Private);
 
   ImporterImpl.availabilityDomainPredicates[var] = funcDecl;
 
diff --git a/test/Availability/Inputs/AvailabilityDomains.c b/test/Availability/Inputs/AvailabilityDomains.c
new file mode 100644
index 0000000000000..a33c881207ee1
--- /dev/null
+++ b/test/Availability/Inputs/AvailabilityDomains.c
@@ -0,0 +1,5 @@
+#include "AvailabilityDomains.h"
+
+int dynamic_domain_pred() {
+	return 1;
+}
diff --git a/test/Availability/Inputs/custom_availability_file1.swift b/test/Availability/Inputs/custom_availability_file1.swift
new file mode 100644
index 0000000000000..7138211ee3e4d
--- /dev/null
+++ b/test/Availability/Inputs/custom_availability_file1.swift
@@ -0,0 +1,15 @@
+@available(DynamicDomain)
+public struct X {
+    public init() { }
+}
+
+public struct Z {
+    public init() {
+        if #available(DynamicDomain) {
+            print("#available")
+            print(X())
+        } else {
+            print("#unavailable")
+        }
+    }
+}
diff --git a/test/Availability/Inputs/custom_availability_file2.swift b/test/Availability/Inputs/custom_availability_file2.swift
new file mode 100644
index 0000000000000..f1d340dd10cbc
--- /dev/null
+++ b/test/Availability/Inputs/custom_availability_file2.swift
@@ -0,0 +1,12 @@
+public struct Y {
+    init() {
+        if #available(DynamicDomain) {
+            print("#available")
+            print(X())
+            print(Z())
+        } else {
+            print("#unavailable")
+            print(Z())
+        }
+    }
+}
diff --git a/test/Availability/availability_custom_domains_clang_build.swift b/test/Availability/availability_custom_domains_clang_build.swift
new file mode 100644
index 0000000000000..6cb43e976b455
--- /dev/null
+++ b/test/Availability/availability_custom_domains_clang_build.swift
@@ -0,0 +1,6 @@
+// REQUIRES: swift_feature_CustomAvailability
+
+// RUN: %empty-directory(%t)
+// RUN: %target-clang -x c %S/Inputs/AvailabilityDomains.c -o %t/AvailabilityDomains.c.o -c
+// RUN: %target-build-swift -emit-library %S/Inputs/custom_availability_file1.swift %S/Inputs/custom_availability_file2.swift -module-name main -enable-experimental-feature CustomAvailability -import-bridging-header %S/Inputs/AvailabilityDomains.h -Xlinker %t/AvailabilityDomains.c.o
+// RUN: %target-build-swift -wmo -emit-library %S/Inputs/custom_availability_file1.swift %S/Inputs/custom_availability_file2.swift -module-name main -enable-experimental-feature CustomAvailability -import-bridging-header %S/Inputs/AvailabilityDomains.h -Xlinker %t/AvailabilityDomains.c.o
diff --git a/test/SILGen/availability_query_custom_domains_clang.swift b/test/SILGen/availability_query_custom_domains_clang.swift
index c13e3b92cc4a1..ccfc6aae16ed4 100644
--- a/test/SILGen/availability_query_custom_domains_clang.swift
+++ b/test/SILGen/availability_query_custom_domains_clang.swift
@@ -101,7 +101,7 @@ public func testIfAvailableDynamicDomain() {
 }
 // CHECK: end sil function '$s4Test28testIfAvailableDynamicDomainyyF'
 
-// CHECK-LABEL: sil hidden [ossa] @$sSC33__swift_DynamicDomain_isAvailableBi1_yF : $@convention(thin) () -> Builtin.Int1
+// CHECK-LABEL: sil private [ossa] @$sSC33__swift_DynamicDomain_isAvailableBi1_yF : $@convention(thin) () -> Builtin.Int1
 // CHECK: bb0:
 // CHECK:   [[QUERY_FUNC:%.*]] = function_ref @$sSo27__DynamicDomain_isAvailableSbyFTo : $@convention(c) () -> Bool
 // CHECK:   [[QUERY_RESULT:%.*]] = apply [[QUERY_FUNC]]() : $@convention(c) () -> Bool