diff --git a/app/src/main/java/org/fdroid/fdroid/views/repos/RepoPreviewScreen.kt b/app/src/main/java/org/fdroid/fdroid/views/repos/RepoPreviewScreen.kt
index 1f65ef343..e8847de09 100644
--- a/app/src/main/java/org/fdroid/fdroid/views/repos/RepoPreviewScreen.kt
+++ b/app/src/main/java/org/fdroid/fdroid/views/repos/RepoPreviewScreen.kt
@@ -45,6 +45,7 @@ import org.fdroid.fdroid.Utils.getGlideModel
 import org.fdroid.fdroid.compose.ComposeUtils.FDroidButton
 import org.fdroid.fdroid.compose.ComposeUtils.FDroidContent
 import org.fdroid.index.v2.FileV2
+import org.fdroid.repo.FetchResult.IsExistingMirror
 import org.fdroid.repo.FetchResult.IsExistingRepository
 import org.fdroid.repo.FetchResult.IsNewMirror
 import org.fdroid.repo.FetchResult.IsNewRepository
@@ -122,6 +123,10 @@ fun RepoPreviewHeader(
                 )
             }
         }
+        if (state.isMirror) Text(
+            text = stringResource(R.string.repo_mirror_add_info),
+            style = MaterialTheme.typography.body2,
+        )
         if (state.canAdd) FDroidButton(
             text = when (state.fetchResult) {
                 is IsNewRepository -> stringResource(R.string.repo_add_new_title)
@@ -129,14 +134,16 @@ fun RepoPreviewHeader(
                 else -> error("Unexpected fetch state: ${state.fetchResult}")
             },
             onClick = onAddRepo,
-            modifier = Modifier.align(End)
-        ) else if (state.fetchResult is IsExistingRepository) {
-            Text(
-                text = stringResource(R.string.repo_exists),
-                style = MaterialTheme.typography.body1,
-                color = MaterialTheme.colors.error,
-            )
-        }
+            modifier = Modifier.align(End),
+        ) else Text(
+            text = when (state.fetchResult) {
+                is IsExistingRepository -> stringResource(R.string.repo_exists)
+                is IsExistingMirror -> stringResource(R.string.repo_mirror_exists)
+                else -> error("Unexpected fetch state: ${state.fetchResult}")
+            },
+            style = MaterialTheme.typography.body1,
+            color = MaterialTheme.colors.error,
+        )
         val description = if (isDevPreview) {
             LoremIpsum(42).values.joinToString(" ")
         } else {
@@ -233,12 +240,11 @@ fun RepoPreviewScreenFetchingPreview() {
 @Composable
 @Preview(uiMode = Configuration.UI_MODE_NIGHT_YES, widthDp = 720, heightDp = 360)
 fun RepoPreviewScreenNewMirrorPreview() {
-    val address = "https://example.org"
-    val repo = FDroidApp.createSwapRepo(address, "foo bar")
+    val repo = FDroidApp.createSwapRepo("https://example.org", "foo bar")
     FDroidContent {
         RepoPreviewScreen(
             PaddingValues(0.dp),
-            Fetching(address, repo, emptyList(), IsNewMirror(0L))
+            Fetching("https://mirror.example.org", repo, emptyList(), IsNewMirror(0L))
         ) {}
     }
 }
@@ -255,3 +261,15 @@ fun RepoPreviewScreenExistingRepoPreview() {
         ) {}
     }
 }
+
+@Preview
+@Composable
+fun RepoPreviewScreenExistingMirrorPreview() {
+    val repo = FDroidApp.createSwapRepo("https://example.org", "foo bar")
+    FDroidContent {
+        RepoPreviewScreen(
+            PaddingValues(0.dp),
+            Fetching("https://mirror.example.org", repo, emptyList(), IsExistingMirror)
+        ) {}
+    }
+}
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index bb2162e5e..6838f262e 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -223,6 +223,8 @@ This often occurs with apps installed via Google Play or other sources, if they
     <string name="repo_io_error">Error connecting to the repository.</string>
     <string name="repo_error_adding_archive">Archive repositories can not be added directly. Tap the repository in the list and enable the archive there.</string>
     <string name="repo_share_not_found">Could not find repo address in shared text.</string>
+    <string name="repo_mirror_exists">This mirror was already added.</string>
+    <string name="repo_mirror_add_info">The URL you are trying to add is a mirror of an existing repository.</string>
     <string name="bad_fingerprint">Bad fingerprint</string>
     <string name="invalid_url">This is not a valid URL.</string>
     <string name="malformed_repo_uri">Ignoring malformed repo URI: %s</string>
diff --git a/libs/database/src/main/java/org/fdroid/repo/RepoAdder.kt b/libs/database/src/main/java/org/fdroid/repo/RepoAdder.kt
index 5a0b000ed..a808619fe 100644
--- a/libs/database/src/main/java/org/fdroid/repo/RepoAdder.kt
+++ b/libs/database/src/main/java/org/fdroid/repo/RepoAdder.kt
@@ -62,8 +62,14 @@ public class Fetching(
     /**
      * true if the repository can be added (be it as new [Repository] or new mirror).
      */
-    public val canAdd: Boolean = repo != null &&
-        (fetchResult != null && fetchResult !is FetchResult.IsExistingRepository)
+    public val canAdd: Boolean = repo != null
+            && fetchResult != null
+            && fetchResult !is FetchResult.IsExistingRepository
+            && fetchResult !is FetchResult.IsExistingMirror
+
+    public val isMirror: Boolean = repo != null
+            && fetchResult != null
+            && (fetchResult is FetchResult.IsNewMirror || fetchResult is FetchResult.IsExistingMirror)
 
     override fun toString(): String {
         return "Fetching(fetchUrl=$fetchUrl, repo=${repo?.address}, apps=${apps.size}, " +
@@ -95,6 +101,7 @@ public sealed class FetchResult {
     public data class IsNewMirror(internal val existingRepoId: Long) : FetchResult()
 
     public data object IsExistingRepository : FetchResult()
+    public data object IsExistingMirror : FetchResult()
 }
 
 @OptIn(DelicateCoroutinesApi::class)
@@ -233,17 +240,15 @@ internal class RepoAdder(
 
         return if (existingRepo == null) {
             FetchResult.IsNewRepository
+        } else if (existingRepo.address.trimEnd('/') == url) {
+            FetchResult.IsExistingRepository
         } else {
-            val existingMirror = if (existingRepo.address.trimEnd('/') == url) {
-                url
-            } else {
-                existingRepo.mirrors.find { it.url.trimEnd('/') == url }
-                    ?: existingRepo.userMirrors.find { it.trimEnd('/') == url }
-            }
+            val existingMirror = existingRepo.mirrors.find { it.url.trimEnd('/') == url }
+                ?: existingRepo.userMirrors.find { it.trimEnd('/') == url }
             if (existingMirror == null) {
                 FetchResult.IsNewMirror(existingRepo.repoId)
             } else {
-                FetchResult.IsExistingRepository
+                FetchResult.IsExistingMirror
             }
         }
     }
@@ -266,7 +271,8 @@ internal class RepoAdder(
             ?: throw IllegalStateException("No fetchResult: ${addRepoState.value}")
 
         val modifiedRepo: Repository = when (fetchResult) {
-            is FetchResult.IsExistingRepository -> error("Unexpected result: $fetchResult")
+            is FetchResult.IsExistingRepository -> error("Repo exists: $fetchResult")
+            is FetchResult.IsExistingMirror -> error("Mirror exists: $fetchResult")
             is FetchResult.IsNewRepository -> {
                 // reset the timestamp of the actual repo,
                 // so a following repo update will pick this up
@@ -283,7 +289,7 @@ internal class RepoAdder(
                     val repoId = repositoryDao.insert(newRepo)
                     // add user mirror, if URL is not the repo address and not a known mirror
                     if (state.fetchUrl != repo.address.trimEnd('/') &&
-                        repo.mirrors.find {state.fetchUrl == it.url.trimEnd('/') } == null
+                        repo.mirrors.find { state.fetchUrl == it.url.trimEnd('/') } == null
                     ) {
                         val userMirrors = listOf(state.fetchUrl)
                         repositoryDao.updateUserMirrors(repoId, userMirrors)
diff --git a/libs/database/src/test/java/org/fdroid/repo/RepoAdderTest.kt b/libs/database/src/test/java/org/fdroid/repo/RepoAdderTest.kt
index ae1c61fff..d2181cbc6 100644
--- a/libs/database/src/test/java/org/fdroid/repo/RepoAdderTest.kt
+++ b/libs/database/src/test/java/org/fdroid/repo/RepoAdderTest.kt
@@ -358,8 +358,11 @@ internal class RepoAdderTest {
         // repo is already in the DB
         every { repoDao.getRepository(any<String>()) } returns existingRepo
 
-        expectMinRepoPreview(repoName, FetchResult.IsExistingRepository, canAdd = false) {
-            repoAdder.fetchRepository(url = url, proxy = null)
+        val expectedFetchResult =
+            if (existingRepo.address == url) FetchResult.IsExistingRepository else FetchResult.IsExistingMirror
+
+        expectMinRepoPreview(repoName, expectedFetchResult, canAdd = false) {
+            repoAdder.fetchRepository(url = downloadUrl, proxy = null)
         }
         assertFailsWith<IllegalStateException> {
             repoAdder.addFetchedRepository()