diff --git a/src/Makefile b/src/Makefile
index f7181ef6..be0d8332 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -9,8 +9,8 @@ BIN = ../prince
 
 OS      := $(shell uname)
 
-CPPFLAGS += -Wall -D_GNU_SOURCE=1
-CFLAGS += -std=gnu99 -O2
+CPPFLAGS += -Wall -D_XOPEN_SOURCE=700
+CFLAGS += -std=c11 -O2
 
 ifeq ($(OS),Darwin)
 LIBS := $(shell sdl2-config --libs) -lSDL2_image
diff --git a/src/midi.c b/src/midi.c
index 3b4923db..12fe0fcc 100644
--- a/src/midi.c
+++ b/src/midi.c
@@ -122,7 +122,7 @@ bool parse_midi(midi_raw_chunk_type* midi, parsed_midi_type* parsed_midi) {
 		printf("Warning: Midi sound does not have any tracks.\n");
 		return 0;
 	}
-	int division = SDL_SwapBE16(midi->header.time_division);
+	int division = SDL_SwapBE16(midi->header.delta);
 	if (division < 0) {
 		division = (-(division / 256)) * (division & 0xFF); // Translate time delta from the alternative SMTPE format.
 	}
@@ -130,7 +130,7 @@ bool parse_midi(midi_raw_chunk_type* midi, parsed_midi_type* parsed_midi) {
 
 	parsed_midi->tracks = calloc(1, num_tracks * sizeof(midi_track_type));
 	parsed_midi->num_tracks = num_tracks;
-	midi_raw_chunk_type* next_track_chunk = (midi_raw_chunk_type*) midi->header.tracks; // The first track chunk starts after the header chunk.
+	midi_raw_chunk_type* next_track_chunk = (midi_raw_chunk_type*) midi->tracks; // The first track chunk starts after the header chunk.
 	byte last_event_type = 0;
 	for (int track_index = 0; track_index < num_tracks; ++track_index) {
 		midi_raw_chunk_type* track_chunk = next_track_chunk;
@@ -140,9 +140,9 @@ bool parse_midi(midi_raw_chunk_type* midi, parsed_midi_type* parsed_midi) {
 			memset(&parsed_midi, 0, sizeof(parsed_midi));
 			return 0;
 		}
-		next_track_chunk = (midi_raw_chunk_type*) (track_chunk->data + (dword) SDL_SwapBE32(track_chunk->chunk_length));
+		next_track_chunk = (midi_raw_chunk_type*) ((byte *)&track_chunk->header.format + (dword) SDL_SwapBE32(track_chunk->chunk_length));
 		midi_track_type* track = &parsed_midi->tracks[track_index];
-		byte* buffer_position = track_chunk->data;
+		byte* buffer_position = (byte *)&track_chunk->header.format;
 		for (;;) {
 			track->events = realloc(track->events, (++track->num_events) * sizeof(midi_event_type));
 			midi_event_type* event = &track->events[track->num_events - 1];
diff --git a/src/types.h b/src/types.h
index ab922e8f..e4b9a438 100644
--- a/src/types.h
+++ b/src/types.h
@@ -546,19 +546,17 @@ typedef struct digi_new_type { // wave in 1.3 and 1.4 (and PoP2)
 } digi_new_type;
 SDL_COMPILE_TIME_ASSERT(digi_new_type, sizeof(digi_new_type) == 9);
 
-typedef struct midi_type {
-	char chunk_type[4];
-	dword chunk_length;
-	union {
-		struct {
+typedef struct midi_type_header {
 			word format;
 			word num_tracks;
 			word delta;
-			byte tracks[0];
-		} header;
-		byte data[0];
-	};
+} midi_type_header;
 
+typedef struct midi_type {
+	char chunk_type[4];
+	dword chunk_length;
+	midi_type_header header;
+	byte tracks[];
 } midi_type;
 
 typedef struct ogg_type {
@@ -589,16 +587,8 @@ typedef struct sound_buffer_type {
 typedef struct midi_raw_chunk_type {
 	char chunk_type[4];
 	dword chunk_length;
-	union {
-		struct {
-			word format;
-			word num_tracks;
-			word time_division;
-			byte tracks[0];
-		} header;
-		byte data[0];
-	};
-
+	midi_type_header header;
+	byte tracks[];
 } midi_raw_chunk_type;
 
 typedef struct midi_event_type {