diff --git a/keystore/java/android/security/keystore/AndroidKeyStoreKeyGeneratorSpi.java b/keystore/java/android/security/keystore/AndroidKeyStoreKeyGeneratorSpi.java
index 419eb24..2d04d72 100644
--- a/keystore/java/android/security/keystore/AndroidKeyStoreKeyGeneratorSpi.java
+++ b/keystore/java/android/security/keystore/AndroidKeyStoreKeyGeneratorSpi.java
@@ -210,6 +210,10 @@
                         throw new InvalidAlgorithmParameterException(
                             "HMAC key size must be at least 64 bits.");
                     }
+                    if (mKeySizeBits > 512 && spec.isStrongBoxBacked()) {
+                        throw new InvalidAlgorithmParameterException(
+                            "StrongBox HMAC key size must be smaller than 512 bits.");
+                    }
 
                     // JCA HMAC key algorithm implies a digest (e.g., HmacSHA256 key algorithm
                     // implies SHA-256 digest). Because keymaster HMAC key is authorized only for
diff --git a/keystore/java/android/security/keystore/AndroidKeyStoreKeyPairGeneratorSpi.java b/keystore/java/android/security/keystore/AndroidKeyStoreKeyPairGeneratorSpi.java
index 5fc742a..d44c894 100644
--- a/keystore/java/android/security/keystore/AndroidKeyStoreKeyPairGeneratorSpi.java
+++ b/keystore/java/android/security/keystore/AndroidKeyStoreKeyPairGeneratorSpi.java
@@ -303,7 +303,7 @@
             if (mKeySizeBits == -1) {
                 mKeySizeBits = getDefaultKeySize(keymasterAlgorithm);
             }
-            checkValidKeySize(keymasterAlgorithm, mKeySizeBits);
+            checkValidKeySize(keymasterAlgorithm, mKeySizeBits, mSpec.isStrongBoxBacked());
 
             if (spec.getKeystoreAlias() == null) {
                 throw new InvalidAlgorithmParameterException("KeyStore entry alias not provided");
@@ -724,10 +724,18 @@
         }
     }
 
-    private static void checkValidKeySize(int keymasterAlgorithm, int keySize)
+    private static void checkValidKeySize(
+            int keymasterAlgorithm,
+            int keySize,
+            boolean isStrongBoxBacked)
             throws InvalidAlgorithmParameterException {
         switch (keymasterAlgorithm) {
             case KeymasterDefs.KM_ALGORITHM_EC:
+                if (isStrongBoxBacked && keySize != 256) {
+                    throw new InvalidAlgorithmParameterException(
+                            "Unsupported StrongBox EC key size: "
+                            + keySize + " bits. Supported: 256");
+                }
                 if (!SUPPORTED_EC_NIST_CURVE_SIZES.contains(keySize)) {
                     throw new InvalidAlgorithmParameterException("Unsupported EC key size: "
                             + keySize + " bits. Supported: " + SUPPORTED_EC_NIST_CURVE_SIZES);