Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -7467,6 +7467,7 @@
     const AvailabilityAttr *AA =
       getAttrForPlatform(SemaRef.getASTContext(), OffendingDecl);
     VersionTuple Introduced = AA->getIntroduced();
+    Introduced.UseDotAsSeparator();
 
     if (AvailabilityStack.back() >= Introduced)
       return;
Index: test/FixIt/fixit-availability-method.mm
===================================================================
--- /dev/null
+++ test/FixIt/fixit-availability-method.mm
@@ -0,0 +1,13 @@
+// RUN: %clang_cc1 -triple x86_64-apple-macosx-10.11 -Wunguarded-availability -fdiagnostics-parseable-fixits -fsyntax-only -verify %s
+
+@interface foo
+- (void) method_bar __attribute__((availability(macosx, introduced = 10_12))); // expected-note {{'method_bar' has been explicitly marked partial here}}
+@end
+
+int main() {
+    [foo method_bar]; // \
+    // expected-warning {{'method_bar' is only available on macOS 10.12 or newer}} \
+    // expected-note {{enclose 'method_bar' in an @available check to silence this warning}} \
+    // CHECK: "fix-it:.*if (@available(macOS 10.12, *))"
+    return 0;
+}