diff --git a/core/cochran.c b/core/cochran.c
index 430c3b48a..fdfb7bf1c 100644
--- a/core/cochran.c
+++ b/core/cochran.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/datatrak.c b/core/datatrak.c
index 272aa3424..15559b043 100644
--- a/core/datatrak.c
+++ b/core/datatrak.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/datatrak.h b/core/datatrak.h
index 3a37e0465..a774c6018 100644
--- a/core/datatrak.h
+++ b/core/datatrak.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef DATATRAK_HEADER_H
 #define DATATRAK_HEADER_H
 
diff --git a/core/deco.c b/core/deco.c
index 88585c98d..7e1a18d3f 100644
--- a/core/deco.c
+++ b/core/deco.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* calculate deco values
  * based on Bühlmann ZHL-16b
  * based on an implemention by heinrichs weikamp for the DR5
diff --git a/core/deco.h b/core/deco.h
index bfedd6046..03b8c59f3 100644
--- a/core/deco.h
+++ b/core/deco.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef DECO_H
 #define DECO_H
 
diff --git a/core/device.c b/core/device.c
index e20aecb5a..25c5136a9 100644
--- a/core/device.c
+++ b/core/device.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <string.h>
 #include "dive.h"
 #include "device.h"
diff --git a/core/device.h b/core/device.h
index 264ea8db5..df069a1d5 100644
--- a/core/device.h
+++ b/core/device.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef DEVICE_H
 #define DEVICE_H
 
diff --git a/core/divelist.c b/core/divelist.c
index f3465830e..fd7fc6790 100644
--- a/core/divelist.c
+++ b/core/divelist.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* divelist.c */
 /* core logic for the dive list -
  * accessed through the following interfaces:
diff --git a/core/divelist.h b/core/divelist.h
index 52ebbada9..74b616890 100644
--- a/core/divelist.h
+++ b/core/divelist.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef DIVELIST_H
 #define DIVELIST_H
 
diff --git a/core/file.c b/core/file.c
index 889a9102b..ba2956d60 100644
--- a/core/file.c
+++ b/core/file.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/stat.h>
diff --git a/core/file.h b/core/file.h
index 1c1dfc116..8c5647ed2 100644
--- a/core/file.h
+++ b/core/file.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef FILE_H
 #define FILE_H
 
diff --git a/core/git-access.c b/core/git-access.c
index 5aca509db..e190e4d5f 100644
--- a/core/git-access.c
+++ b/core/git-access.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/git-access.h b/core/git-access.h
index b8b8181fe..5cdef37ae 100644
--- a/core/git-access.h
+++ b/core/git-access.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef GITACCESS_H
 #define GITACCESS_H
 
diff --git a/core/libdivecomputer.c b/core/libdivecomputer.c
index cd52866fa..ec8b456f7 100644
--- a/core/libdivecomputer.c
+++ b/core/libdivecomputer.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/libdivecomputer.h b/core/libdivecomputer.h
index b8f69282a..19f09fdfa 100644
--- a/core/libdivecomputer.h
+++ b/core/libdivecomputer.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef LIBDIVECOMPUTER_H
 #define LIBDIVECOMPUTER_H
 
diff --git a/core/linux.c b/core/linux.c
index 5c9726750..9f8121d09 100644
--- a/core/linux.c
+++ b/core/linux.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* linux.c */
 /* implements Linux specific functions */
 #include "dive.h"
diff --git a/core/liquivision.c b/core/liquivision.c
index c42086403..fb2b44446 100644
--- a/core/liquivision.c
+++ b/core/liquivision.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <string.h>
 
 #include "dive.h"
diff --git a/core/macos.c b/core/macos.c
index a7272599b..6af474e85 100644
--- a/core/macos.c
+++ b/core/macos.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* macos.c */
 /* implements Mac OS X specific functions */
 #include <stdlib.h>
diff --git a/core/membuffer.c b/core/membuffer.c
index e35f160b2..aa08bb5ea 100644
--- a/core/membuffer.c
+++ b/core/membuffer.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/membuffer.h b/core/membuffer.h
index 434b34c71..fd59d7140 100644
--- a/core/membuffer.h
+++ b/core/membuffer.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef MEMBUFFER_H
 #define MEMBUFFER_H
 
diff --git a/core/parse-xml.c b/core/parse-xml.c
index 75fa49df2..129914e3c 100644
--- a/core/parse-xml.c
+++ b/core/parse-xml.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/planner.c b/core/planner.c
index f9acc155d..69ac24efa 100644
--- a/core/planner.c
+++ b/core/planner.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* planner.c
  *
  * code that allows us to plan future dives
diff --git a/core/planner.h b/core/planner.h
index 919fddac8..3cae87cac 100644
--- a/core/planner.h
+++ b/core/planner.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef PLANNER_H
 #define PLANNER_H
 
diff --git a/core/pref.h b/core/pref.h
index 9cefd0812..14699153e 100644
--- a/core/pref.h
+++ b/core/pref.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef PREF_H
 #define PREF_H
 
diff --git a/core/prefs-macros.h b/core/prefs-macros.h
index fe459d3da..bd1fc9a33 100644
--- a/core/prefs-macros.h
+++ b/core/prefs-macros.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef PREFSMACROS_H
 #define PREFSMACROS_H
 
diff --git a/core/save-git.c b/core/save-git.c
index 30cb2972f..6916dec33 100644
--- a/core/save-git.c
+++ b/core/save-git.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/save-html.c b/core/save-html.c
index 2824625ef..be9b3a0f8 100644
--- a/core/save-html.c
+++ b/core/save-html.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/save-html.h b/core/save-html.h
index 13bb102b1..8bcc38799 100644
--- a/core/save-html.h
+++ b/core/save-html.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef HTML_SAVE_H
 #define HTML_SAVE_H
 
diff --git a/core/save-xml.c b/core/save-xml.c
index b6a0e4b81..b80481ed9 100644
--- a/core/save-xml.c
+++ b/core/save-xml.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/statistics.c b/core/statistics.c
index 5f0d977e7..47e65ff72 100644
--- a/core/statistics.c
+++ b/core/statistics.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* statistics.c
  *
  * core logic for the Info & Stats page -
diff --git a/core/statistics.h b/core/statistics.h
index 732ae79cd..97aa4334c 100644
--- a/core/statistics.h
+++ b/core/statistics.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * statistics.h
  *
diff --git a/core/strndup.h b/core/strndup.h
index 84e18b60f..4bdd19301 100644
--- a/core/strndup.h
+++ b/core/strndup.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef STRNDUP_H
 #define STRNDUP_H
 #if __WIN32__
diff --git a/core/strtod.c b/core/strtod.c
index 81e5d42d1..f0170ac3b 100644
--- a/core/strtod.c
+++ b/core/strtod.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * Sane helper for 'strtod()'.
  *
diff --git a/core/subsurfacestartup.c b/core/subsurfacestartup.c
index c2ab42583..a686ceab7 100644
--- a/core/subsurfacestartup.c
+++ b/core/subsurfacestartup.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include "subsurfacestartup.h"
 #include "version.h"
 #include <stdbool.h>
diff --git a/core/subsurfacestartup.h b/core/subsurfacestartup.h
index 53d44f28d..fcabb4f6c 100644
--- a/core/subsurfacestartup.h
+++ b/core/subsurfacestartup.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef SUBSURFACESTARTUP_H
 #define SUBSURFACESTARTUP_H
 
diff --git a/core/time.c b/core/time.c
index cbf7d2e2a..7b8a6ff0f 100644
--- a/core/time.c
+++ b/core/time.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <string.h>
 #include "dive.h"
 
diff --git a/core/uemis-downloader.c b/core/uemis-downloader.c
index 6bf2dcabf..79c88d28b 100644
--- a/core/uemis-downloader.c
+++ b/core/uemis-downloader.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * uemis-downloader.c
  *
diff --git a/core/uemis.c b/core/uemis.c
index 199b69fa1..e48ab0c92 100644
--- a/core/uemis.c
+++ b/core/uemis.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: MIT
 /*
  * uemis.c
  *
diff --git a/core/uemis.h b/core/uemis.h
index 1758b4b32..28af7832d 100644
--- a/core/uemis.h
+++ b/core/uemis.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /*
  * defines and prototypes for the uemis Zurich SDA file parser
  */
diff --git a/core/windows.c b/core/windows.c
index c767cbeda..6a852bf6f 100644
--- a/core/windows.c
+++ b/core/windows.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 /* windows.c */
 /* implements Windows specific functions */
 #include <io.h>
diff --git a/core/worldmap-options.h b/core/worldmap-options.h
index 177443563..6d5fe1119 100644
--- a/core/worldmap-options.h
+++ b/core/worldmap-options.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef WORLDMAP_OPTIONS_H
 #define WORLDMAP_OPTIONS_H
 
diff --git a/core/worldmap-save.c b/core/worldmap-save.c
index 8ad6535ba..a48e376a1 100644
--- a/core/worldmap-save.c
+++ b/core/worldmap-save.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifdef __clang__
 // Clang has a bug on zero-initialization of C structs.
 #pragma clang diagnostic ignored "-Wmissing-field-initializers"
diff --git a/core/worldmap-save.h b/core/worldmap-save.h
index 102ea40e5..d20b6684b 100644
--- a/core/worldmap-save.h
+++ b/core/worldmap-save.h
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #ifndef WORLDMAP_SAVE_H
 #define WORLDMAP_SAVE_H