diff --git a/src/io.cpp b/src/io.cpp
index 5bce92909..2cba76aa1 100644
--- a/src/io.cpp
+++ b/src/io.cpp
@@ -29,6 +29,7 @@
 #include <fastgltf/core.hpp>
 
 #if defined(__APPLE__) || defined(__linux__)
+#include <fcntl.h>
 #include <unistd.h>
 #include <sys/file.h>
 #include <sys/mman.h>