diff --git a/clang/lib/Driver/ToolChains/Darwin.cpp b/clang/lib/Driver/ToolChains/Darwin.cpp
index 17d57b2f7eedab4..e576efaf5ca884c 100644
--- a/clang/lib/Driver/ToolChains/Darwin.cpp
+++ b/clang/lib/Driver/ToolChains/Darwin.cpp
@@ -2953,7 +2953,15 @@ static bool sdkSupportsBuiltinModules(
   case Darwin::MacOS:
     return SDKVersion >= VersionTuple(15U);
   case Darwin::IPhoneOS:
-    return SDKVersion >= VersionTuple(18U);
+    switch (TargetEnvironment) {
+    case Darwin::MacCatalyst:
+      // Mac Catalyst uses `-target arm64-apple-ios18.0-macabi` so the platform
+      // is iOS, but it builds with the macOS SDK, so it's the macOS SDK version
+      // that's relevant.
+      return SDKVersion >= VersionTuple(15U);
+    default:
+      return SDKVersion >= VersionTuple(18U);
+    }
   case Darwin::TvOS:
     return SDKVersion >= VersionTuple(18U);
   case Darwin::WatchOS:
diff --git a/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json b/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json
index 77b70e1a83c19ce..ced45d5c2199623 100644
--- a/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json
+++ b/clang/test/Driver/Inputs/MacOSX15.0.sdk/SDKSettings.json
@@ -1 +1 @@
-{"Version":"990.0", "MaximumDeploymentTarget": "99.0.99"}
+{"Version":"15.0", "MaximumDeploymentTarget": "15.0.99"}
diff --git a/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json b/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json
new file mode 100644
index 000000000000000..d46295b2ab5a17e
--- /dev/null
+++ b/clang/test/Driver/Inputs/MacOSX15.1.sdk/SDKSettings.json
@@ -0,0 +1 @@
+{"Version":"15.1", "MaximumDeploymentTarget": "15.1.99"}
diff --git a/clang/test/Driver/darwin-builtin-modules.c b/clang/test/Driver/darwin-builtin-modules.c
index ec515133be8aba2..4564d7317d7abe2 100644
--- a/clang/test/Driver/darwin-builtin-modules.c
+++ b/clang/test/Driver/darwin-builtin-modules.c
@@ -8,5 +8,8 @@
 
 // RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-macos14.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
 // RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-macos15.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.0.sdk -target x86_64-apple-ios18.0-macabi -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.1.sdk -target x86_64-apple-macos15.1 -darwin-target-variant x86_64-apple-ios18.1-macabi -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
+// RUN: %clang -isysroot %S/Inputs/MacOSX15.1.sdk -target x86_64-apple-ios18.1-macabi -darwin-target-variant x86_64-apple-macos15.1 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
 // RUN: %clang -isysroot %S/Inputs/DriverKit23.0.sdk -target arm64-apple-driverkit23.0 -### %s 2>&1 | FileCheck --check-prefix=CHECK_FUTURE %s
 // CHECK_FUTURE-NOT: -fbuiltin-headers-in-system-modules