diff --git a/arch/x86_64/idt.c b/arch/x86_64/idt.c
index f49e207..f692f52 100644
--- a/arch/x86_64/idt.c
+++ b/arch/x86_64/idt.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/assert.h>
 #include <zinnia/compiler.h>
 #include <zinnia/irq.h>
diff --git a/arch/x86_64/irq.c b/arch/x86_64/irq.c
index 72f01d3..97c95b9 100644
--- a/arch/x86_64/irq.c
+++ b/arch/x86_64/irq.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/alloc.h>
 #include <zinnia/assert.h>
 #include <zinnia/percpu.h>
diff --git a/arch/x86_64/serial.c b/arch/x86_64/serial.c
index b5adc94..845430e 100644
--- a/arch/x86_64/serial.c
+++ b/arch/x86_64/serial.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/console.h>
 #include <zinnia/init.h>
 #include <zinnia/initgraph.h>
diff --git a/dev/acpi/init.c b/dev/acpi/init.c
index 9904866..e2f7824 100644
--- a/dev/acpi/init.c
+++ b/dev/acpi/init.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #define pr_fmt(fmt) "acpi: " fmt
 
 #include <zinnia/acpi.h>
diff --git a/dev/acpi/uacpi_glue.c b/dev/acpi/uacpi_glue.c
index baad859..c3ad765 100644
--- a/dev/acpi/uacpi_glue.c
+++ b/dev/acpi/uacpi_glue.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/acpi.h>
 #include <zinnia/alloc.h>
 #include <zinnia/console.h>
diff --git a/dev/block/nvme/pci.c b/dev/block/nvme/pci.c
index 1b9b9e7..1efd5d1 100644
--- a/dev/block/nvme/pci.c
+++ b/dev/block/nvme/pci.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/errno.h>
 #include <zinnia/module.h>
 #include <zinnia/pci.h>
diff --git a/dev/pci/core.c b/dev/pci/core.c
index bd65e55..dadc76d 100644
--- a/dev/pci/core.c
+++ b/dev/pci/core.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #define pr_fmt(fmt) "pci: " fmt
 
 #include <zinnia/alloc.h>
diff --git a/dev/video/fbcon/fbcon.c b/dev/video/fbcon/fbcon.c
index 2a7460b..62f3c22 100644
--- a/dev/video/fbcon/fbcon.c
+++ b/dev/video/fbcon/fbcon.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/alloc.h>
 #include <zinnia/assert.h>
 #include <zinnia/console.h>
diff --git a/lib/console.c b/lib/console.c
index 68adfe8..05d19ca 100644
--- a/lib/console.c
+++ b/lib/console.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/console.h>
 #include <zinnia/init.h>
 #include <zinnia/print.h>
diff --git a/lib/irq.c b/lib/irq.c
index d621c3a..1b16360 100644
--- a/lib/irq.c
+++ b/lib/irq.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/assert.h>
 #include <zinnia/irq.h>
 #include <zinnia/list.h>
diff --git a/lib/print.c b/lib/print.c
index d2a12cd..4565965 100644
--- a/lib/print.c
+++ b/lib/print.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/clock.h>
 #include <zinnia/console.h>
 #include <zinnia/panic.h>
diff --git a/syscalls/dispatch.c b/syscalls/dispatch.c
index e5b2fa5..81f7463 100644
--- a/syscalls/dispatch.c
+++ b/syscalls/dispatch.c
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: ISC
+
 #include <zinnia/compiler.h>
 #include <zinnia/errno.h>
 #include <zinnia/print.h>