diff --git a/testsuite/tests/mmap/c_support.c b/testsuite/tests/mmap/c_support.c
index 6af0acf5..883a1851 100644
--- a/testsuite/tests/mmap/c_support.c
+++ b/testsuite/tests/mmap/c_support.c
@@ -2,6 +2,7 @@
 #include <stdio.h>
 #include <unistd.h>
 #include <sys/stat.h>
+#include <fcntl.h>
 
 /* We don't use standard lseek implementation on Windows otherwise
  * creating very large file will be inefficient as mingw lseek will