diff --git a/solana-kotlin/src/commonMain/kotlin/net/avianlabs/solana/domain/core/AccountKeysList.kt b/solana-kotlin/src/commonMain/kotlin/net/avianlabs/solana/domain/core/AccountKeysList.kt
index 3a7312a..8b58bd7 100644
--- a/solana-kotlin/src/commonMain/kotlin/net/avianlabs/solana/domain/core/AccountKeysList.kt
+++ b/solana-kotlin/src/commonMain/kotlin/net/avianlabs/solana/domain/core/AccountKeysList.kt
@@ -5,10 +5,12 @@ public class AccountKeysList {
 
   public fun add(accountMeta: AccountMeta) {
     val key = accountMeta.publicKey.toString()
-    if (accounts.containsKey(key)) {
-      if (!accounts[key]!!.isWritable && accountMeta.isWritable) {
-        accounts[key] = accountMeta
-      }
+    val existing = accounts[key]
+    if (existing != null) {
+      accounts[key] = existing.copy(
+        isSigner = accountMeta.isSigner || existing.isSigner,
+        isWritable = accountMeta.isWritable || existing.isWritable,
+      )
     } else {
       accounts[key] = accountMeta
     }
diff --git a/solana-kotlin/src/commonTest/kotlin/net/avianlabs/solana/domain/core/AccountKeysListTest.kt b/solana-kotlin/src/commonTest/kotlin/net/avianlabs/solana/domain/core/AccountKeysListTest.kt
new file mode 100644
index 0000000..0ba8d68
--- /dev/null
+++ b/solana-kotlin/src/commonTest/kotlin/net/avianlabs/solana/domain/core/AccountKeysListTest.kt
@@ -0,0 +1,22 @@
+package net.avianlabs.solana.domain.core
+
+import kotlin.test.Test
+import kotlin.test.assertTrue
+
+class AccountKeysListTest {
+  @Test
+  fun add_different_writable_flags_preserves_isSigner() {
+    val accountKeysList = AccountKeysList()
+    val accountMeta1 = AccountMeta(PublicKey.fromBase58("4rZoSK72jVaAW1ayZLrefdMPAAStRVhCfH1PSundaoNt"), false, true)
+
+    accountKeysList.add(accountMeta1)
+
+    val accountMeta2 = AccountMeta(PublicKey.fromBase58("4rZoSK72jVaAW1ayZLrefdMPAAStRVhCfH1PSundaoNt"), true, false)
+
+    accountKeysList.add(accountMeta2)
+
+    assertTrue(accountKeysList.list.size == 1)
+    assertTrue(accountKeysList.list[0].isSigner)
+    assertTrue(accountKeysList.list[0].isWritable)
+  }
+}