diff --git a/app/src/main/java/com/wireguard/android/ConfigEditFragment.java b/app/src/main/java/com/wireguard/android/ConfigEditFragment.java
index a8e37155..488d7915 100644
--- a/app/src/main/java/com/wireguard/android/ConfigEditFragment.java
+++ b/app/src/main/java/com/wireguard/android/ConfigEditFragment.java
@@ -4,8 +4,6 @@ import android.content.Context;
 import android.os.Bundle;
 import android.text.InputFilter;
 import android.text.LoginFilter;
-import android.text.SpannableStringBuilder;
-import android.text.Spanned;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuInflater;
@@ -17,7 +15,6 @@ import android.widget.EditText;
 
 import com.wireguard.android.databinding.ConfigEditFragmentBinding;
 import com.wireguard.config.Config;
-import com.wireguard.crypto.KeyEncoding;
 
 /**
  * Fragment for editing a WireGuard configuration.
@@ -58,39 +55,7 @@ public class ConfigEditFragment extends BaseConfigFragment {
                 }
         });
         final EditText privateKeyText = binding.getRoot().findViewById(R.id.private_key_text);
-        privateKeyText.setFilters(new InputFilter[]{
-                new InputFilter() {
-                    @Override
-                    public CharSequence filter(final CharSequence source,
-                                               final int sStart, final int sEnd,
-                                               final Spanned dest,
-                                               final int dStart, final int dEnd) {
-                        SpannableStringBuilder replacement = null;
-                        int rIndex = 0;
-                        final int dLength = dest.length();
-                        for (int sIndex = sStart; sIndex < sEnd; ++sIndex) {
-                            final char c = source.charAt(sIndex);
-                            final int dIndex = dStart + (sIndex - sStart);
-                            // Restrict characters to the base64 character set.
-                            // Ensure adding this character does not push the length over the limit.
-                            if (((dIndex + 1 < KeyEncoding.KEY_LENGTH_BASE64 && isAllowed(c)) ||
-                                    (dIndex + 1 == KeyEncoding.KEY_LENGTH_BASE64 && c == '=')) &&
-                                    dLength + (sIndex - sStart) < KeyEncoding.KEY_LENGTH_BASE64) {
-                                ++rIndex;
-                            } else {
-                                if (replacement == null)
-                                    replacement = new SpannableStringBuilder(source, sStart, sEnd);
-                                replacement.delete(rIndex, rIndex + 1);
-                            }
-                        }
-                        return replacement;
-                    }
-
-                    private boolean isAllowed(final char c) {
-                        return Character.isLetterOrDigit(c) || c == '+' || c == '/';
-                    }
-                }
-        });
+        privateKeyText.setFilters(new InputFilter[]{new KeyInputFilter()});
         binding.setConfig(localConfig);
         return binding.getRoot();
     }
diff --git a/app/src/main/java/com/wireguard/android/KeyInputFilter.java b/app/src/main/java/com/wireguard/android/KeyInputFilter.java
new file mode 100644
index 00000000..758528c9
--- /dev/null
+++ b/app/src/main/java/com/wireguard/android/KeyInputFilter.java
@@ -0,0 +1,42 @@
+package com.wireguard.android;
+
+import android.text.InputFilter;
+import android.text.SpannableStringBuilder;
+import android.text.Spanned;
+
+import com.wireguard.crypto.KeyEncoding;
+
+/**
+ * InputFilter for entering WireGuard private/public keys encoded with base64.
+ */
+class KeyInputFilter implements InputFilter {
+    @Override
+    public CharSequence filter(final CharSequence source,
+                               final int sStart, final int sEnd,
+                               final Spanned dest,
+                               final int dStart, final int dEnd) {
+        SpannableStringBuilder replacement = null;
+        int rIndex = 0;
+        final int dLength = dest.length();
+        for (int sIndex = sStart; sIndex < sEnd; ++sIndex) {
+            final char c = source.charAt(sIndex);
+            final int dIndex = dStart + (sIndex - sStart);
+            // Restrict characters to the base64 character set.
+            // Ensure adding this character does not push the length over the limit.
+            if (((dIndex + 1 < KeyEncoding.KEY_LENGTH_BASE64 && isAllowed(c)) ||
+                    (dIndex + 1 == KeyEncoding.KEY_LENGTH_BASE64 && c == '=')) &&
+                    dLength + (sIndex - sStart) < KeyEncoding.KEY_LENGTH_BASE64) {
+                ++rIndex;
+            } else {
+                if (replacement == null)
+                    replacement = new SpannableStringBuilder(source, sStart, sEnd);
+                replacement.delete(rIndex, rIndex + 1);
+            }
+        }
+        return replacement;
+    }
+
+    private boolean isAllowed(final char c) {
+        return Character.isLetterOrDigit(c) || c == '+' || c == '/';
+    }
+}