diff --git a/corefoundation.go b/corefoundation.go
index 224f1ee..e5cc226 100644
--- a/corefoundation.go
+++ b/corefoundation.go
@@ -43,6 +43,12 @@ func Release(ref C.CFTypeRef) {
 	C.CFRelease(ref)
 }
 
+// releaseCFDictionary releases a CFDictionaryRef. Wrapper around a C function
+// for testing (cgo is not supported directly in _test.go files).
+func releaseCFDictionary(d C.CFDictionaryRef) {
+	Release(C.CFTypeRef(d))
+}
+
 // BytesToCFData will return a CFDataRef and if non-nil, must be released with
 // Release(ref).
 func BytesToCFData(b []byte) (C.CFDataRef, error) {
diff --git a/ios.go b/ios.go
index 9332508..403c16f 100644
--- a/ios.go
+++ b/ios.go
@@ -20,3 +20,12 @@ var accessibleTypeRef = map[Accessible]C.CFTypeRef{
 	AccessibleAfterFirstUnlockThisDeviceOnly: C.CFTypeRef(C.kSecAttrAccessibleAfterFirstUnlockThisDeviceOnly),
 	AccessibleAccessibleAlwaysThisDeviceOnly: C.CFTypeRef(C.kSecAttrAccessibleAlwaysThisDeviceOnly),
 }
+
+// UseDataProtectionKeychainKey has no effect on iOS, where the data protection
+// keychain is the only keychain. It is defined for cross-platform API parity
+// and is always empty.
+var UseDataProtectionKeychainKey string
+
+// SetUseDataProtectionKeychain is a no-op on iOS, where the data protection
+// keychain is the only keychain. It is defined for cross-platform API parity.
+func (*Item) SetUseDataProtectionKeychain(_ bool) {}
diff --git a/keychain_test.go b/keychain_test.go
new file mode 100644
index 0000000..26c2f7e
--- /dev/null
+++ b/keychain_test.go
@@ -0,0 +1,73 @@
+//go:build darwin && !ios
+
+package keychain
+
+import (
+	"testing"
+)
+
+func TestUseDataProtectionKeychainKey(t *testing.T) {
+	if !dataProtectionKeychainAvailable() {
+		// On macOS < 10.15 the key is intentionally empty (see macos.go).
+		if UseDataProtectionKeychainKey != "" {
+			t.Fatalf("expected empty key on macOS < 10.15, got %q", UseDataProtectionKeychainKey)
+		}
+		t.Skip("kSecUseDataProtectionKeychain unavailable (macOS < 10.15)")
+	}
+
+	// On macOS 10.15+ the kSecUseDataProtectionKeychain binding must resolve to
+	// a non-empty key. An empty key here would mean the cgo binding or the
+	// __builtin_available guard in macos.go is broken.
+	if UseDataProtectionKeychainKey == "" {
+		t.Fatal("UseDataProtectionKeychainKey is empty on macOS 10.15+; kSecUseDataProtectionKeychain binding failed")
+	}
+}
+
+func TestSetUseDataProtectionKeychain(t *testing.T) {
+	if UseDataProtectionKeychainKey == "" {
+		t.Skip("kSecUseDataProtectionKeychain unavailable (macOS < 10.15)")
+	}
+
+	item := NewItem()
+	if _, ok := item.attr[UseDataProtectionKeychainKey]; ok {
+		t.Fatal("expected no data protection attribute on a fresh item")
+	}
+
+	item.SetUseDataProtectionKeychain(true)
+	v, ok := item.attr[UseDataProtectionKeychainKey]
+	if !ok {
+		t.Fatal("expected data protection attribute to be set")
+	}
+	if v != true {
+		t.Fatalf("expected attribute value true, got %v", v)
+	}
+
+	item.SetUseDataProtectionKeychain(false)
+	v, ok = item.attr[UseDataProtectionKeychainKey]
+	if !ok {
+		t.Fatal("expected data protection attribute to remain set when false")
+	}
+	if v != false {
+		t.Fatalf("expected attribute value false, got %v", v)
+	}
+}
+
+func TestUseDataProtectionKeychainConvertsToCFDictionary(t *testing.T) {
+	if UseDataProtectionKeychainKey == "" {
+		t.Skip("kSecUseDataProtectionKeychain unavailable (macOS < 10.15)")
+	}
+
+	item := NewItem()
+	item.SetSecClass(SecClassGenericPassword)
+	item.SetService("TestUseDataProtectionKeychain")
+	item.SetAccount("test")
+	item.SetUseDataProtectionKeychain(true)
+
+	// Exercises the bool -> CFBoolean marshalling path for the new key
+	// without touching the real keychain.
+	cfDict, err := ConvertMapToCFDictionary(item.attr)
+	if err != nil {
+		t.Fatalf("ConvertMapToCFDictionary failed: %v", err)
+	}
+	releaseCFDictionary(cfDict)
+}
diff --git a/macos.go b/macos.go
index f2597ee..bfef6d8 100644
--- a/macos.go
+++ b/macos.go
@@ -7,6 +7,30 @@ package keychain
 #cgo LDFLAGS: -framework CoreFoundation -framework Security
 #include <CoreFoundation/CoreFoundation.h>
 #include <Security/Security.h>
+
+// goKeychainUseDataProtectionKeychainKey returns kSecUseDataProtectionKeychain
+// when running on macOS 10.15 or later. That symbol is annotated
+// API_AVAILABLE(macos(10.15)), so on older systems it is weak-imported and is
+// NULL at runtime. The __builtin_available guard ensures we only read it when
+// it actually exists; otherwise referencing it during package init would pass
+// NULL to CFStringToString and crash the whole package.
+static CFStringRef goKeychainUseDataProtectionKeychainKey(void) {
+	if (__builtin_available(macOS 10.15, *)) {
+		return kSecUseDataProtectionKeychain;
+	}
+	return NULL;
+}
+
+// goKeychainDataProtectionKeychainAvailable reports whether the running macOS
+// version provides the data protection keychain (macOS 10.15+). It checks the
+// OS version directly rather than inferring it from whether the key resolved,
+// so callers can distinguish "OS too old" from "binding broken".
+static int goKeychainDataProtectionKeychainAvailable(void) {
+	if (__builtin_available(macOS 10.15, *)) {
+		return 1;
+	}
+	return 0;
+}
 */
 import "C"
 
@@ -25,3 +49,35 @@ var (
 		// AccessibleWhenPasscodeSetThisDeviceOnly:  C.CFTypeRef(C.kSecAttrAccessibleWhenPasscodeSetThisDeviceOnly),
 	}
 )
+
+// UseDataProtectionKeychainKey is the attribute key for
+// kSecUseDataProtectionKeychain. It is empty on macOS versions older than
+// 10.15, where that key is unavailable.
+var UseDataProtectionKeychainKey = resolveUseDataProtectionKeychainKey()
+
+func resolveUseDataProtectionKeychainKey() string {
+	ref := C.goKeychainUseDataProtectionKeychainKey()
+	if ref == 0 {
+		return ""
+	}
+	return CFStringToString(ref)
+}
+
+// dataProtectionKeychainAvailable reports whether the running macOS version
+// (10.15+) provides the kSecUseDataProtectionKeychain key.
+func dataProtectionKeychainAvailable() bool {
+	return C.goKeychainDataProtectionKeychainAvailable() != 0
+}
+
+// SetUseDataProtectionKeychain controls whether the operation targets the data
+// protection keychain (the iOS-style keychain) instead of the legacy
+// file-based keychain. The two are separate stores, so this should be set
+// consistently across the add, query, update, and delete calls for an item.
+// Requires macOS 10.15+; on older versions the kSecUseDataProtectionKeychain
+// key is unavailable and this is a no-op.
+func (k *Item) SetUseDataProtectionKeychain(b bool) {
+	if UseDataProtectionKeychainKey == "" {
+		return
+	}
+	k.attr[UseDataProtectionKeychainKey] = b
+}