diff --git a/include/Makefile.in b/include/Makefile.in
index 99d74bae..4d8a59e5 100644
--- a/include/Makefile.in
+++ b/include/Makefile.in
@@ -506,6 +506,7 @@ SOURCES = \
 	msvcrt/setjmp.h \
 	msvcrt/share.h \
 	msvcrt/signal.h \
+	msvcrt/stdarg.h \
 	msvcrt/stdbool.h \
 	msvcrt/stddef.h \
 	msvcrt/stdint.h \
@@ -521,6 +522,7 @@ SOURCES = \
 	msvcrt/time.h \
 	msvcrt/uchar.h \
 	msvcrt/unistd.h \
+	msvcrt/vadefs.h \
 	msvcrt/wchar.h \
 	msvcrt/wctype.h \
 	mswsock.h \
diff --git a/include/msvcrt/stdarg.h b/include/msvcrt/stdarg.h
new file mode 100644
index 00000000..6c6b6048
--- /dev/null
+++ b/include/msvcrt/stdarg.h
@@ -0,0 +1,31 @@
+/*
+ * Variable argument definitions
+ *
+ * Copyright 2022 Jacek Caban
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#ifndef _INC_STDARG
+#define _INC_STDARG
+
+#include <vadefs.h>
+
+#define va_start(v,l)  _crt_va_start(v,l)
+#define va_arg(v,l)    _crt_va_arg(v,l)
+#define va_end(v)      _crt_va_end(v)
+#define va_copy(d,s)   _crt_va_copy(d,s)
+
+#endif /* _INC_STDARG */
diff --git a/include/msvcrt/vadefs.h b/include/msvcrt/vadefs.h
new file mode 100644
index 00000000..2a612fc0
--- /dev/null
+++ b/include/msvcrt/vadefs.h
@@ -0,0 +1,52 @@
+/*
+ * Variable argument definitions
+ *
+ * Copyright 2022 Jacek Caban
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
+ */
+
+#ifndef _INC_VADEFS
+#define _INC_VADEFS
+
+#ifdef __cplusplus
+#define _ADDRESSOF(v) (&reinterpret_cast<const char &>(v))
+#else
+#define _ADDRESSOF(v) (&(v))
+#endif
+
+#if defined(__GNUC__) || defined(__clang__)
+
+typedef __builtin_va_list va_list;
+#define _crt_va_start(v,l)  __builtin_va_start(v,l)
+#define _crt_va_arg(v,l)    __builtin_va_arg(v,l)
+#define _crt_va_end(v)      __builtin_va_end(v)
+#define _crt_va_copy(d,s)   __builtin_va_copy(d,s)
+
+#else
+
+typedef char *va_list;
+
+#if defined(__i386__)
+#define _INTSIZEOF(n) ((sizeof(n) + sizeof(int) - 1) & ~(sizeof(int) - 1))
+#define _crt_va_start(v,l)  ((v) = (va_list)_ADDRESSOF(l) + _INTSIZEOF(l))
+#define _crt_va_arg(v,l)    (*(l *)(((v) += _INTSIZEOF(l)) - _INTSIZEOF(l)))
+#define _crt_va_end(v)      ((v) = (va_list)0)
+#define _crt_va_copy(d,s)   ((d) = (s))
+#endif
+
+#endif
+
+#endif /* _INC_VADEFS */