diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/algorithm/negotiation/SymmetricKeyAlgorithmNegotiator.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/algorithm/negotiation/SymmetricKeyAlgorithmNegotiator.kt
index d11f2c03..63cc6a59 100644
--- a/pgpainless-core/src/main/kotlin/org/pgpainless/algorithm/negotiation/SymmetricKeyAlgorithmNegotiator.kt
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/algorithm/negotiation/SymmetricKeyAlgorithmNegotiator.kt
@@ -4,7 +4,6 @@
 
 package org.pgpainless.algorithm.negotiation
 
-import java.lang.IllegalArgumentException
 import org.pgpainless.algorithm.SymmetricKeyAlgorithm
 import org.pgpainless.policy.Policy
 
@@ -36,9 +35,8 @@ interface SymmetricKeyAlgorithmNegotiator {
                     override: SymmetricKeyAlgorithm?,
                     keyPreferences: List<Set<SymmetricKeyAlgorithm>>
                 ): SymmetricKeyAlgorithm {
-                    if (override == SymmetricKeyAlgorithm.NULL) {
-                        throw IllegalArgumentException(
-                            "Algorithm override cannot be NULL (plaintext).")
+                    require (override != SymmetricKeyAlgorithm.NULL) {
+                        "Algorithm override cannot be NULL (plaintext)."
                     }
 
                     if (override != null) {
diff --git a/pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionOptions.kt b/pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionOptions.kt
index a52c4722..96258b9b 100644
--- a/pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionOptions.kt
+++ b/pgpainless-core/src/main/kotlin/org/pgpainless/encryption_signing/EncryptionOptions.kt
@@ -405,6 +405,10 @@ class EncryptionOptions(private val purpose: EncryptionPurpose, private val api:
     }
 
     fun overrideEncryptionMechanism(encryptionMechanism: MessageEncryptionMechanism) = apply {
+        require(api.algorithmPolicy.symmetricKeyEncryptionAlgorithmPolicy.isAcceptable(
+            encryptionMechanism.symmetricKeyAlgorithm)) {
+            "Provided symmetric encryption algorithm is not acceptable."
+        }
         _encryptionMechanismOverride = encryptionMechanism
     }