diff --git a/app/src/main/java/be/chvp/nanoledger/data/LedgerRepository.kt b/app/src/main/java/be/chvp/nanoledger/data/LedgerRepository.kt
index 777de5c..89cefa9 100644
--- a/app/src/main/java/be/chvp/nanoledger/data/LedgerRepository.kt
+++ b/app/src/main/java/be/chvp/nanoledger/data/LedgerRepository.kt
@@ -88,19 +88,39 @@ class LedgerRepository
             fileUri: Uri,
             text: String,
             onFinish: suspend () -> Unit,
+            onMismatch: suspend () -> Unit,
             onWriteError: suspend (IOException) -> Unit,
             onReadError: suspend (IOException) -> Unit,
         ) {
             try {
-                context.contentResolver.openOutputStream(fileUri, "wa")
-                    ?.let { OutputStreamWriter(it) }
-                    ?.use {
-                        if (!fileContents.value!!.isEmpty() && fileContents.value!!.last() != "") {
-                            it.write("\n")
+                val result = ArrayList<String>()
+                fileUri
+                    .let { context.contentResolver.openInputStream(it) }
+                    ?.let { BufferedReader(InputStreamReader(it)) }
+                    ?.use { reader ->
+                        var line = reader.readLine()
+                        while (line != null) {
+                            result.add(line)
+                            line = reader.readLine()
                         }
-                        it.write(text)
                     }
-                readFrom(fileUri, onFinish, onReadError)
+
+                if (!result.equals(fileContents.value)) {
+                    onMismatch()
+                } else {
+                    context.contentResolver.openOutputStream(fileUri, "w")
+                        ?.let { OutputStreamWriter(it) }
+                        ?.use {
+                            fileContents.value!!.forEach { line ->
+                                it.write("${line}\n")
+                            }
+                            if (!fileContents.value!!.isEmpty() && fileContents.value!!.last() != "") {
+                                it.write("\n")
+                            }
+                            it.write(text)
+                        }
+                    readFrom(fileUri, onFinish, onReadError)
+                }
             } catch (e: IOException) {
                 onWriteError(e)
             }
diff --git a/app/src/main/java/be/chvp/nanoledger/ui/add/AddActivity.kt b/app/src/main/java/be/chvp/nanoledger/ui/add/AddActivity.kt
index a91dc4f..610320b 100644
--- a/app/src/main/java/be/chvp/nanoledger/ui/add/AddActivity.kt
+++ b/app/src/main/java/be/chvp/nanoledger/ui/add/AddActivity.kt
@@ -7,6 +7,7 @@ import android.content.Context
 import android.content.Intent
 import android.os.Bundle
 import android.util.Log
+import android.widget.Toast
 import androidx.activity.ComponentActivity
 import androidx.activity.compose.BackHandler
 import androidx.activity.compose.setContent
@@ -84,11 +85,12 @@ class AddActivity() : ComponentActivity() {
         setContent {
             val context = LocalContext.current
             val latestError by addViewModel.latestError.observeAsState()
-            val errorMessage = stringResource(R.string.error_writing_file)
             val showMessage = stringResource(R.string.show)
             val scope = rememberCoroutineScope()
             val snackbarHostState = remember { SnackbarHostState() }
             var openErrorDialog by rememberSaveable { mutableStateOf(false) }
+
+            val errorMessage = stringResource(R.string.error_writing_file)
             var errorDialogMessage by rememberSaveable { mutableStateOf("") }
             LaunchedEffect(latestError) {
                 val error = latestError?.get()
@@ -108,6 +110,20 @@ class AddActivity() : ComponentActivity() {
                     }
                 }
             }
+
+            val latestMismatch by addViewModel.latestMismatch.observeAsState()
+            val mismatchMessage = stringResource(R.string.mismatch_no_write)
+            LaunchedEffect(latestMismatch) {
+                val error = latestMismatch?.get()
+                if (error != null) {
+                    Toast.makeText(
+                        context,
+                        mismatchMessage,
+                        Toast.LENGTH_LONG,
+                    ).show()
+                }
+            }
+
             BackHandler(enabled = true) {
                 finish()
                 startActivity(
diff --git a/app/src/main/java/be/chvp/nanoledger/ui/add/AddViewModel.kt b/app/src/main/java/be/chvp/nanoledger/ui/add/AddViewModel.kt
index a164c24..2bd8802 100644
--- a/app/src/main/java/be/chvp/nanoledger/ui/add/AddViewModel.kt
+++ b/app/src/main/java/be/chvp/nanoledger/ui/add/AddViewModel.kt
@@ -105,6 +105,9 @@ class AddViewModel
         private val _latestError = MutableLiveData<Event<IOException>?>(null)
         val latestError: LiveData<Event<IOException>?> = _latestError
 
+        private val _latestMismatch = MutableLiveData<Event<Int>?>(null)
+        val latestMismatch: LiveData<Event<Int>?> = _latestMismatch
+
         val currencyBeforeAmount: LiveData<Boolean> = preferencesDataSource.currencyBeforeAmount
 
         fun append(onFinish: suspend () -> Unit) {
@@ -146,6 +149,10 @@ class AddViewModel
                             _saving.postValue(false)
                             onFinish()
                         },
+                        {
+                            _saving.postValue(false)
+                            _latestMismatch.postValue(Event(1))
+                        },
                         {
                             _saving.postValue(false)
                             _latestError.postValue(Event(it))
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 555baed..6001a62 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -18,6 +18,7 @@
     <string name="error">Error</string>
     <string name="error_reading_file">Error while reading file</string>
     <string name="error_writing_file">Error while writing file</string>
+    <string name="mismatch_no_write">File contents outdated, aborting write</string>
     <string name="mismatch_no_delete">File contents outdated, aborting delete</string>
     <string name="file">File</string>
     <string name="note">Note</string>