diff --git a/i18n/en/noctua.ftl b/i18n/en/noctua.ftl
index 46ba213..8a3c741 100644
--- a/i18n/en/noctua.ftl
+++ b/i18n/en/noctua.ftl
@@ -1,4 +1,4 @@
-# SPDX-License-Identifier: MPL-2.0
+# SPDX-License-Identifier: GPL-3.0-or-later
 # i18n/en/noctua.ftl
 #
 # Localization strings for Noctua's user interface (English).
diff --git a/resources/app.metainfo.xml b/resources/app.metainfo.xml
index ae1bb74..08e598b 100644
--- a/resources/app.metainfo.xml
+++ b/resources/app.metainfo.xml
@@ -1,4 +1,4 @@
-<!-- SPDX-License-Identifier: MPL-2.0 -->
+<!-- SPDX-License-Identifier: GPL-3.0-or-later -->
 <!-- resources/app.metainfo.xml -->
 <!-- AppStream metadata for software centers (e.g., COSMIC Store, GNOME Software, KDE Discover). -->
 
diff --git a/resources/icons/hicolor/scalable/apps/noctua.svg b/resources/icons/hicolor/scalable/apps/noctua.svg
index a9afad6..9bc0588 100644
--- a/resources/icons/hicolor/scalable/apps/noctua.svg
+++ b/resources/icons/hicolor/scalable/apps/noctua.svg
@@ -1,4 +1,4 @@
-<!-- SPDX-License-Identifier: MPL-2.0 -->
+<!-- SPDX-License-Identifier: GPL-3.0-or-later -->
 <!-- resources/icons/hicolor/scalable/apps/org.noctua.Noctua.svg -->
 <!-- Stylized owl icon for Noctua, with one eye as a document/magnifying glass. -->
 
diff --git a/src/app/document/file.rs b/src/app/document/file.rs
index f3bceda..d7bc4cf 100644
--- a/src/app/document/file.rs
+++ b/src/app/document/file.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/file.rs
 //
 // Opening files and dispatching to the correct concrete document type.
diff --git a/src/app/document/meta.rs b/src/app/document/meta.rs
index cef8b38..fb6ef8c 100644
--- a/src/app/document/meta.rs
+++ b/src/app/document/meta.rs
@@ -1,2 +1,2 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/meta.rs
diff --git a/src/app/document/mod.rs b/src/app/document/mod.rs
index 4ce68bb..d4e438b 100644
--- a/src/app/document/mod.rs
+++ b/src/app/document/mod.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/mod.rs
 //
 // Document module root: common enums and type erasure for document kinds.
diff --git a/src/app/document/portable.rs b/src/app/document/portable.rs
index 8f60a64..0acf00d 100644
--- a/src/app/document/portable.rs
+++ b/src/app/document/portable.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/portable.rs
 //
 // Portable documents (e.g. PDF) – basic model and rendering stub.
diff --git a/src/app/document/raster.rs b/src/app/document/raster.rs
index a8e5092..c12a617 100644
--- a/src/app/document/raster.rs
+++ b/src/app/document/raster.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/raster.rs
 
 use std::path::PathBuf;
diff --git a/src/app/document/transform.rs b/src/app/document/transform.rs
index 641ddf3..2b410c0 100644
--- a/src/app/document/transform.rs
+++ b/src/app/document/transform.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/transform.rs
 //
 // High-level document transformations (rotate, flip, etc.).
diff --git a/src/app/document/utils.rs b/src/app/document/utils.rs
index 5fb2dbc..2271d98 100644
--- a/src/app/document/utils.rs
+++ b/src/app/document/utils.rs
@@ -1,2 +1,2 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/utils.rs
diff --git a/src/app/document/vector.rs b/src/app/document/vector.rs
index 8512450..b2dea19 100644
--- a/src/app/document/vector.rs
+++ b/src/app/document/vector.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/document/vector.rs
 //
 // Vector documents (SVG, etc.).
diff --git a/src/app/message.rs b/src/app/message.rs
index 1cddaa0..fd6ab97 100644
--- a/src/app/message.rs
+++ b/src/app/message.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/message.rs
 //
 // Top-level application messages (events, IO, and UI signals).
diff --git a/src/app/mod.rs b/src/app/mod.rs
index 59cb735..28394f3 100644
--- a/src/app/mod.rs
+++ b/src/app/mod.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MIT OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/mod.rs
 //
 // Application module root, re-exports, and COSMIC application wiring.
diff --git a/src/app/model.rs b/src/app/model.rs
index 734c280..ebfe75d 100644
--- a/src/app/model.rs
+++ b/src/app/model.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MIT OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/model.rs
 //
 // Global application state.
diff --git a/src/app/update.rs b/src/app/update.rs
index 1311ce7..78d44f1 100644
--- a/src/app/update.rs
+++ b/src/app/update.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0 OR Apache-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/update.rs
 //
 // Application update loop: applies messages to the global model state.
diff --git a/src/app/view/canvas.rs b/src/app/view/canvas.rs
index d17ce20..82e5c99 100644
--- a/src/app/view/canvas.rs
+++ b/src/app/view/canvas.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/view/canvas.rs
 //
 // Center canvas for displaying the current document.
diff --git a/src/app/view/mod.rs b/src/app/view/mod.rs
index 1f07b1f..59997cd 100644
--- a/src/app/view/mod.rs
+++ b/src/app/view/mod.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/view/mod.rs
 //
 // Root layout for the main application window.
diff --git a/src/app/view/panels.rs b/src/app/view/panels.rs
index 6104961..5875d4f 100644
--- a/src/app/view/panels.rs
+++ b/src/app/view/panels.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/app/view/panels.rs
 //
 // Header, footer, and side panels composing the main layout.
diff --git a/src/config.rs b/src/config.rs
index a3237d0..6102270 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/config.rs
 
 use cosmic::cosmic_config::{self, CosmicConfigEntry, cosmic_config_derive::CosmicConfigEntry};
diff --git a/src/i18n.rs b/src/i18n.rs
index 65782d6..153facf 100644
--- a/src/i18n.rs
+++ b/src/i18n.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/i18n.rs
 
 use i18n_embed::{
diff --git a/src/main.rs b/src/main.rs
index a483179..65ed240 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,4 @@
-// SPDX-License-Identifier: MPL-2.0
+// SPDX-License-Identifier: GPL-3.0-or-later
 // src/main.rs
 
 mod app;