diff --git a/include/FMI.h b/include/FMI.h
index e6535c21..d015094a 100644
--- a/include/FMI.h
+++ b/include/FMI.h
@@ -13,6 +13,7 @@ extern "C" {
 
 #include <stdbool.h>
 #include <stddef.h>
+#include <stdarg.h>
 
 #ifndef FMI_MAX_MESSAGE_LENGTH
 #define FMI_MAX_MESSAGE_LENGTH 4096