diff --git a/src/org/fdroid/fdroid/views/fragments/RepoListFragment.java b/src/org/fdroid/fdroid/views/fragments/RepoListFragment.java
index 7f04bd64f..07ae9a41f 100644
--- a/src/org/fdroid/fdroid/views/fragments/RepoListFragment.java
+++ b/src/org/fdroid/fdroid/views/fragments/RepoListFragment.java
@@ -364,7 +364,8 @@ public class RepoListFragment extends ListFragment
             final Button addButton = alrt.getButton(DialogInterface.BUTTON_POSITIVE);
             alrt.setTitle(R.string.repo_exists);
             overwriteMessage.setVisibility(View.VISIBLE);
-            newFingerprint = newFingerprint.toUpperCase(Locale.ENGLISH);
+            if (newFingerprint != null)
+                newFingerprint = newFingerprint.toUpperCase(Locale.ENGLISH);
             if (repo.fingerprint == null && newFingerprint != null) {
                 // we're upgrading from unsigned to signed repo
                 overwriteMessage.setText(R.string.repo_exists_add_fingerprint);