diff --git a/app/src/main/java/org/fdroid/fdroid/Preferences.java b/app/src/main/java/org/fdroid/fdroid/Preferences.java
index 955b431e5..0e9e4f2b6 100644
--- a/app/src/main/java/org/fdroid/fdroid/Preferences.java
+++ b/app/src/main/java/org/fdroid/fdroid/Preferences.java
@@ -597,10 +597,17 @@ public final class Preferences implements SharedPreferences.OnSharedPreferenceCh
     private String intMapToString(HashMap<String, Integer> intMap) {
         String output = "";
         for (String key : intMap.keySet()) {
-            if (!output.isEmpty()) {
-                output = output + "\n";
+            Integer value = intMap.get(key);
+            if (key == null || key.isEmpty()) {
+                Utils.debugLog(TAG, "Don't serialize record with null key");
+            } else if (value == null) {
+                Utils.debugLog(TAG, "Don't serialize null value for: " + key);
+            } else {
+                if (!output.isEmpty()) {
+                    output = output + "\n";
+                }
+                output = output + key + " " + value;
             }
-            output = output + key + " " + intMap.get(key);
         }
         return output;
     }
@@ -612,17 +619,21 @@ public final class Preferences implements SharedPreferences.OnSharedPreferenceCh
             // values may be missing or unparseable
             String key = pair[0];
             Integer value = 0;
-            if (pair.length > 1) {
-                try {
-                    value = Integer.valueOf(pair[1]);
-                } catch (NumberFormatException e) {
-                    // use default value if stored value can't be parsed
-                    Utils.debugLog(TAG, "Serialized map entry value can't be parsed: " + line);
+            if (key != null && !key.isEmpty()) {
+                if (pair.length > 1) {
+                    try {
+                        value = Integer.valueOf(pair[1]);
+                    } catch (NumberFormatException e) {
+                        // use default value if stored value can't be parsed
+                        Utils.debugLog(TAG, "Serialized map entry value can't be parsed: " + line);
+                    }
+                } else {
+                    Utils.debugLog(TAG, "Serialized map entry value is missing: " + line);
                 }
+                output.put(key, value);
             } else {
-                Utils.debugLog(TAG, "Serialized map entry value is missing: " + line);
+                Utils.debugLog(TAG, "Serialized map entry key is missing: " + line);
             }
-            output.put(key, value);
         }
         return output;
     }
diff --git a/app/src/test/java/org/fdroid/fdroid/PreferencesTest.java b/app/src/test/java/org/fdroid/fdroid/PreferencesTest.java
index 31266cdaf..2eaf48e4a 100644
--- a/app/src/test/java/org/fdroid/fdroid/PreferencesTest.java
+++ b/app/src/test/java/org/fdroid/fdroid/PreferencesTest.java
@@ -20,6 +20,7 @@ package org.fdroid.fdroid;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 import android.content.Context;
@@ -35,6 +36,7 @@ import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
 import org.robolectric.shadows.ShadowLog;
 
+import java.util.HashMap;
 import java.util.Map;
 
 @RunWith(RobolectricTestRunner.class)
@@ -157,4 +159,16 @@ public class PreferencesTest {
         assertNotEquals(Long.parseLong(defaults.getString(Preferences.PREF_KEEP_CACHE_TIME, null)),
                 Preferences.get().getKeepCacheTime());
     }
+
+    @Test
+    public void testMirrorErrorMethods() {
+        Preferences.setupForTests(CONTEXT);
+        Preferences preferences = Preferences.get();
+        // serialize an empty map
+        preferences.setMirrorErrorData(new HashMap<>(0));
+        HashMap<String, Integer> result = preferences.getMirrorErrorData();
+        // deserializing should return an empty map without throwing any exceptions
+        assertNotNull(result);
+        assertEquals(result.size(), 0);
+    }
 }