diff --git a/src/audio_file.cc b/src/audio_file.cc
index d9001de..89805e9 100644
--- a/src/audio_file.cc
+++ b/src/audio_file.cc
@@ -6,9 +6,9 @@
 #include "sound.h"
 
 #include <assert.h>
-#include <io.h>
 #include <stdio.h>
 #include <string.h>
+#include <filesystem>
 
 // 0x5108C0
 AudioFileIsCompressedProc* _queryCompressedFunc_2 = _defaultCompressionFunc__;
@@ -100,7 +100,7 @@ int audioFileOpen(const char* fname, int flags, ...)
         audioFile->soundDecoder = soundDecoderInit(audioFileSoundDecoderReadHandler, audioFile->fileHandle, &(audioFile->field_14), &(audioFile->field_10), &(audioFile->fileSize));
         audioFile->fileSize *= 2;
     } else {
-        audioFile->fileSize = filelength(fileno(stream));
+        audioFile->fileSize = std::filesystem::file_size(path);
     }
 
     audioFile->position = 0;
diff --git a/src/cache.cc b/src/cache.cc
index e6ed0b3..e2c77f3 100644
--- a/src/cache.cc
+++ b/src/cache.cc
@@ -5,6 +5,7 @@
 #include "sound.h"
 
 #include <limits.h>
+#include <stdlib.h> // qsort
 #include <stdio.h>
 #include <string.h>
 
diff --git a/src/dfile.cc b/src/dfile.cc
index 2332c46..f83f77c 100644
--- a/src/dfile.cc
+++ b/src/dfile.cc
@@ -5,10 +5,10 @@
 #include <fpattern.h>
 
 #include <assert.h>
-#include <io.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <filesystem>
 
 // Reads .DAT file contents.
 //
@@ -32,7 +32,7 @@ DBase* dbaseOpen(const char* filePath)
 
     // Get file size, and reposition stream to read footer, which contains two
     // 32-bits ints.
-    int fileSize = filelength(fileno(stream));
+    int fileSize = std::filesystem::file_size(filePath);
     if (fseek(stream, fileSize - sizeof(int) * 2, SEEK_SET) != 0) {
         goto err;
     }
diff --git a/src/game.cc b/src/game.cc
index eeeb359..1cc632f 100644
--- a/src/game.cc
+++ b/src/game.cc
@@ -56,7 +56,12 @@
 #include "window_manager.h"
 #include "world_map.h"
 
+#ifdef _WIN32
 #include <io.h>
+#else
+#include <unistd.h> // access
+#endif
+
 #include <stdio.h>
 
 #define HELP_SCREEN_WIDTH (640)
diff --git a/src/xfile.cc b/src/xfile.cc
index ed667ae..95ca375 100644
--- a/src/xfile.cc
+++ b/src/xfile.cc
@@ -418,7 +418,9 @@ long xfileGetSize(XFile* stream)
         fileSize = 0;
         break;
     default:
-        fileSize = filelength(fileno(stream->file));
+        fseek(stream->file, 0L, SEEK_END);
+        fileSize = ftell(stream->file);
+        rewind(stream->file);
         break;
     }