diff --git a/legacy/storage/src/main/java/com/fsck/k9/storage/messages/SaveMessageOperations.kt b/legacy/storage/src/main/java/com/fsck/k9/storage/messages/SaveMessageOperations.kt
index 1490ae8966b..23dd03105e5 100644
--- a/legacy/storage/src/main/java/com/fsck/k9/storage/messages/SaveMessageOperations.kt
+++ b/legacy/storage/src/main/java/com/fsck/k9/storage/messages/SaveMessageOperations.kt
@@ -426,8 +426,7 @@ internal class SaveMessageOperations(
         }
 
         return if (replaceMessageId != null) {
-            values.put("id", replaceMessageId)
-            database.replace("messages", null, values)
+            database.update("messages", values, "id = ?", arrayOf(replaceMessageId.toString()))
             replaceMessageId
         } else {
             database.insert("messages", null, values)
diff --git a/legacy/storage/src/test/java/com/fsck/k9/storage/messages/SaveMessageOperationsTest.kt b/legacy/storage/src/test/java/com/fsck/k9/storage/messages/SaveMessageOperationsTest.kt
index fe8fd7c86b2..ba20d70fd73 100644
--- a/legacy/storage/src/test/java/com/fsck/k9/storage/messages/SaveMessageOperationsTest.kt
+++ b/legacy/storage/src/test/java/com/fsck/k9/storage/messages/SaveMessageOperationsTest.kt
@@ -379,6 +379,46 @@ class SaveMessageOperationsTest : RobolectricTest() {
         assertThat(thread.messageId).isEqualTo(message.id)
     }
 
+    @Test
+    fun `replace envelope message with full message should preserve thread entry`() {
+        // Arrange: simulate remote search saving a message as ENVELOPE (no body)
+        val envelopeMessageData = buildMessage {
+            header("Message-ID", "<msg0001@domain.example>")
+            header("Subject", "Search Result")
+        }.toSaveMessageData(
+            downloadState = MessageDownloadState.ENVELOPE,
+        )
+        saveMessageOperations.saveRemoteMessage(folderId = 1, messageServerId = "uid1", envelopeMessageData)
+
+        val threadsBeforeReplace = sqliteDatabase.readThreads()
+        assertThat(threadsBeforeReplace).hasSize(1)
+        val threadBeforeReplace = threadsBeforeReplace.first()
+
+        // Act: simulate sync re-downloading the same message as FULL
+        val fullMessageData = buildMessage {
+            header("Message-ID", "<msg0001@domain.example>")
+            header("Subject", "Search Result")
+            textBody("Full body content")
+        }.toSaveMessageData(
+            downloadState = MessageDownloadState.FULL,
+        )
+        saveMessageOperations.saveRemoteMessage(folderId = 1, messageServerId = "uid1", fullMessageData)
+
+        // Assert: thread entry must still exist and point to the same message
+        val messages = sqliteDatabase.readMessages()
+        assertThat(messages).hasSize(1)
+        val message = messages.first()
+        assertThat(message.flags).isEqualTo("X_DOWNLOADED_FULL")
+
+        val threads = sqliteDatabase.readThreads()
+        assertThat(threads).hasSize(1)
+        val thread = threads.first()
+        assertThat(thread.id).isEqualTo(threadBeforeReplace.id)
+        assertThat(thread.messageId).isEqualTo(message.id)
+        assertThat(thread.root).isEqualTo(thread.id)
+        assertThat(thread.parent).isNull()
+    }
+
     @Test
     fun `save local message`() {
         val messageData = buildMessage {