diff --git a/app/src/processing/app/SketchController.java b/app/src/processing/app/SketchController.java
index 81af6e1b0..7dae0d8f1 100644
--- a/app/src/processing/app/SketchController.java
+++ b/app/src/processing/app/SketchController.java
@@ -41,6 +41,7 @@ import java.io.File;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Paths;
+import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.Optional;
@@ -448,13 +449,13 @@ public class SketchController {
     }
 
     // rename .pde files to .ino
-    File mainFile = new File(sketch.getMainFilePath());
-    File mainFolder = mainFile.getParentFile();
-    File[] pdeFiles = mainFolder.listFiles((dir, name) -> {
-      return name.toLowerCase().endsWith(".pde");
-    });
+    List<SketchFile> oldFiles = new ArrayList<>();
+    for (SketchFile file : sketch.getFiles()) {
+      if (file.isExtension(Sketch.OLD_SKETCH_EXTENSIONS))
+        oldFiles.add(file);
+    }
 
-    if (pdeFiles != null && pdeFiles.length > 0) {
+    if (oldFiles.size() > 0) {
       if (PreferencesData.get("editor.update_extension") == null) {
         Object[] options = {tr("OK"), tr("Cancel")};
         int result = JOptionPane.showOptionDialog(editor,
@@ -479,8 +480,10 @@ public class SketchController {
 
       if (PreferencesData.getBoolean("editor.update_extension")) {
         // Do rename of all .pde files to new .ino extension
-        for (File pdeFile : pdeFiles)
-          renameCodeToInoExtension(pdeFile);
+        for (SketchFile file : oldFiles) {
+          File newName = FileUtils.replaceExtension(file.getFile(), Sketch.DEFAULT_SKETCH_EXTENSION);
+          file.renameTo(newName);
+        }
       }
     }
 
@@ -488,20 +491,6 @@ public class SketchController {
     return true;
   }
 
-
-  private boolean renameCodeToInoExtension(File pdeFile) {
-    for (SketchFile file : sketch.getFiles()) {
-      if (!file.getFile().equals(pdeFile))
-        continue;
-
-      String pdeName = pdeFile.getPath();
-      pdeName = pdeName.substring(0, pdeName.length() - 4) + ".ino";
-      return file.renameTo(new File(pdeName));
-    }
-    return false;
-  }
-
-
   /**
    * Handles 'Save As' for a sketch.
    * <P>
diff --git a/arduino-core/src/processing/app/Sketch.java b/arduino-core/src/processing/app/Sketch.java
index 704364b88..134fb1f02 100644
--- a/arduino-core/src/processing/app/Sketch.java
+++ b/arduino-core/src/processing/app/Sketch.java
@@ -14,9 +14,9 @@ import static processing.app.I18n.tr;
  * This represents a single sketch, consisting of one or more files.
  */
 public class Sketch {
-
   public static final String DEFAULT_SKETCH_EXTENSION = "ino";
-  public static final List<String> SKETCH_EXTENSIONS = Arrays.asList(DEFAULT_SKETCH_EXTENSION, "pde");
+  public static final List<String> OLD_SKETCH_EXTENSIONS = Arrays.asList("pde");
+  public static final List<String> SKETCH_EXTENSIONS = Stream.concat(Stream.of(DEFAULT_SKETCH_EXTENSION), OLD_SKETCH_EXTENSIONS.stream()).collect(Collectors.toList());
   public static final List<String> OTHER_ALLOWED_EXTENSIONS = Arrays.asList("c", "cpp", "h", "hh", "hpp", "s");
   public static final List<String> EXTENSIONS = Stream.concat(SKETCH_EXTENSIONS.stream(), OTHER_ALLOWED_EXTENSIONS.stream()).collect(Collectors.toList());
 
diff --git a/arduino-core/src/processing/app/helpers/FileUtils.java b/arduino-core/src/processing/app/helpers/FileUtils.java
index 4083a0a69..a4fdb53e7 100644
--- a/arduino-core/src/processing/app/helpers/FileUtils.java
+++ b/arduino-core/src/processing/app/helpers/FileUtils.java
@@ -245,6 +245,26 @@ public class FileUtils {
     return extensions.contains(extension.toLowerCase());
   }
 
+  /**
+   * Returns the given filename with the extension replaced by the one
+   * given. If the filename does not have an extension yet, one is
+   * added.
+   */
+  public static String replaceExtension(String filename, String extension) {
+    SplitFile split = splitFilename(filename);
+    split.extension = extension;
+    return split.join();
+  }
+
+  /**
+   * Returns the given filename with the extension replaced by the one
+   * given. If the filename does not have an extension yet, one is
+   * added.
+   */
+  public static File replaceExtension(File file, String extension) {
+    return new File(file.getParentFile(), replaceExtension(file.getName(), extension));
+  }
+
   /**
    * The result of a splitFilename call.
    */
@@ -256,6 +276,13 @@ public class FileUtils {
 
     public String basename;
     public String extension;
+
+    public String join() {
+      if (extension.equals(""))
+        return basename;
+      else
+        return basename + "." + extension;
+    }
   }
 
   /**