diff --git a/src/action.c b/src/action.c
index 6e2b4bbb..ce735af6 100644
--- a/src/action.c
+++ b/src/action.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <strings.h>
 #include <wlr/util/log.h>
 #include "common/spawn.h"
diff --git a/src/common/spawn.c b/src/common/spawn.c
index f3ee2d79..d8d0abd4 100644
--- a/src/common/spawn.c
+++ b/src/common/spawn.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <glib.h>
diff --git a/src/common/string-helpers.c b/src/common/string-helpers.c
index 3a2205f4..8513ee0c 100644
--- a/src/common/string-helpers.c
+++ b/src/common/string-helpers.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <ctype.h>
 #include <stdio.h>
 #include <string.h>
diff --git a/src/common/zfree.c b/src/common/zfree.c
index 106a6285..3eb399a1 100644
--- a/src/common/zfree.c
+++ b/src/common/zfree.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <stdlib.h>
 #include "common/zfree.h"
 
diff --git a/src/config/keybind.c b/src/config/keybind.c
index 91490928..d26082bc 100644
--- a/src/config/keybind.c
+++ b/src/config/keybind.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <glib.h>
 #include <stdio.h>
diff --git a/src/config/mousebind.c b/src/config/mousebind.c
index 7ed47b45..bafab7a8 100644
--- a/src/config/mousebind.c
+++ b/src/config/mousebind.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <linux/input-event-codes.h>
diff --git a/src/config/rcxml.c b/src/config/rcxml.c
index feec78f5..470a6c9f 100644
--- a/src/config/rcxml.c
+++ b/src/config/rcxml.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <ctype.h>
diff --git a/src/config/session.c b/src/config/session.c
index fcf794f9..a7d6cb23 100644
--- a/src/config/session.c
+++ b/src/config/session.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <ctype.h>
 #include <stdbool.h>
diff --git a/src/cursor.c b/src/cursor.c
index bdc7fc03..2f1c0e13 100644
--- a/src/cursor.c
+++ b/src/cursor.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <assert.h>
 #include <linux/input-event-codes.h>
 #include <sys/time.h>
diff --git a/src/damage.c b/src/damage.c
index 49d97962..3a1e52c6 100644
--- a/src/damage.c
+++ b/src/damage.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "labwc.h"
 
 void
diff --git a/src/desktop.c b/src/desktop.c
index 4479816e..5c229f4f 100644
--- a/src/desktop.c
+++ b/src/desktop.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "config.h"
 #include <assert.h>
 #include "labwc.h"
diff --git a/src/foreign.c b/src/foreign.c
index 73644944..64a03c9b 100644
--- a/src/foreign.c
+++ b/src/foreign.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "labwc.h"
 
 static void
diff --git a/src/interactive.c b/src/interactive.c
index 250f4710..daa6764d 100644
--- a/src/interactive.c
+++ b/src/interactive.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "labwc.h"
 
 void
diff --git a/src/keyboard.c b/src/keyboard.c
index 97437cb7..7c9fc7a7 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <wlr/backend/multi.h>
 #include <wlr/backend/session.h>
 #include "labwc.h"
diff --git a/src/layers.c b/src/layers.c
index 434399a3..2eca01c3 100644
--- a/src/layers.c
+++ b/src/layers.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * layers.c - layer-shell implementation
  *
diff --git a/src/main.c b/src/main.c
index 6b88464d..435010d1 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "common/font.h"
 #include "common/spawn.h"
 #include "config/session.h"
diff --git a/src/menu/menu.c b/src/menu/menu.c
index 54a2b83a..e226a516 100644
--- a/src/menu/menu.c
+++ b/src/menu/menu.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include <assert.h>
 #include <ctype.h>
diff --git a/src/osd.c b/src/osd.c
index 375dad93..6af99473 100644
--- a/src/osd.c
+++ b/src/osd.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "config.h"
 #include <cairo.h>
 #include <drm_fourcc.h>
diff --git a/src/output.c b/src/output.c
index ab0fd289..78d90c6c 100644
--- a/src/output.c
+++ b/src/output.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * output.c: labwc output and rendering
  *
diff --git a/src/seat.c b/src/seat.c
index bcab494b..a5e83239 100644
--- a/src/seat.c
+++ b/src/seat.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <assert.h>
 #include <wlr/backend/libinput.h>
 #include <wlr/util/log.h>
diff --git a/src/server.c b/src/server.c
index c66a2660..02bdff5f 100644
--- a/src/server.c
+++ b/src/server.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #define _POSIX_C_SOURCE 200809L
 #include "config.h"
 #include <signal.h>
diff --git a/src/subsurface.c b/src/subsurface.c
index be00b845..b37cabda 100644
--- a/src/subsurface.c
+++ b/src/subsurface.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2020 the sway authors
  * This file is only needed in support of tracking damage
diff --git a/src/theme.c b/src/theme.c
index 88a62d48..784fdfee 100644
--- a/src/theme.c
+++ b/src/theme.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Theme engine for labwc
  *
diff --git a/src/view-child.c b/src/view-child.c
index 322888eb..dbb30596 100644
--- a/src/view-child.c
+++ b/src/view-child.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2020 the sway authors
  * This file is only needed in support of tracking damage
diff --git a/src/view.c b/src/view.c
index 0c657020..530753a9 100644
--- a/src/view.c
+++ b/src/view.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <stdio.h>
 #include <strings.h>
 #include "labwc.h"
diff --git a/src/xbm/parse.c b/src/xbm/parse.c
index 5589ae26..fdb5b07f 100644
--- a/src/xbm/parse.c
+++ b/src/xbm/parse.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Parse xbm token to create pixmap
  *
diff --git a/src/xbm/tokenize.c b/src/xbm/tokenize.c
index eff2c266..ff6bc73b 100644
--- a/src/xbm/tokenize.c
+++ b/src/xbm/tokenize.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * XBM file tokenizer
  *
diff --git a/src/xbm/xbm.c b/src/xbm/xbm.c
index 9ea540aa..63f0ee1c 100644
--- a/src/xbm/xbm.c
+++ b/src/xbm/xbm.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Create wlr textures based on xbm data
  *
diff --git a/src/xdg-deco.c b/src/xdg-deco.c
index 1bbe36cf..c4e4b572 100644
--- a/src/xdg-deco.c
+++ b/src/xdg-deco.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "labwc.h"
 
 struct xdg_deco {
diff --git a/src/xdg-popup.c b/src/xdg-popup.c
index 1d2f7bba..de5a925e 100644
--- a/src/xdg-popup.c
+++ b/src/xdg-popup.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2020 the sway authors
  *
diff --git a/src/xdg.c b/src/xdg.c
index aa74f813..1eff1640 100644
--- a/src/xdg.c
+++ b/src/xdg.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <assert.h>
 #include "labwc.h"
 #include "ssd.h"
diff --git a/src/xwayland-unmanaged.c b/src/xwayland-unmanaged.c
index 67c5acfc..b5c5922a 100644
--- a/src/xwayland-unmanaged.c
+++ b/src/xwayland-unmanaged.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include "labwc.h"
 
 static void
diff --git a/src/xwayland.c b/src/xwayland.c
index bc021356..edb81eee 100644
--- a/src/xwayland.c
+++ b/src/xwayland.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0-only
 #include <assert.h>
 #include "labwc.h"
 #include "ssd.h"