diff --git a/include/Xprintf.h b/include/Xprintf.h
index 382e24f63f..30aecdc9cf 100644
--- a/include/Xprintf.h
+++ b/include/Xprintf.h
@@ -53,8 +53,5 @@
 extern _X_EXPORT int /* deprecated */
 XNFasprintf(char **ret, const char *_X_RESTRICT_KYWD fmt, ...)
 _X_ATTRIBUTE_PRINTF(2, 3);
-extern _X_EXPORT int
-XNFvasprintf(char **ret, const char *_X_RESTRICT_KYWD fmt, va_list va)
-_X_ATTRIBUTE_VPRINTF(2, 0);
 
 #endif                          /* XPRINTF_H */
diff --git a/os/xprintf.c b/os/xprintf.c
index 1fe1259d60..194c6f1e7b 100644
--- a/os/xprintf.c
+++ b/os/xprintf.c
@@ -67,6 +67,9 @@
 #include "include/os.h"
 #include "include/Xprintf.h"
 
+static int XNFvasprintf(char **ret, const char *_X_RESTRICT_KYWD fmt, va_list va)
+_X_ATTRIBUTE_PRINTF(2, 0);
+
 /**
  * Varargs sprintf that allocates a string buffer the right size for
  * the pattern & data provided and prints the requested data to it.
@@ -78,7 +81,7 @@
  * @param va      variable argument list
  * @return        size of allocated buffer
  */
-int
+static int
 XNFvasprintf(char **ret, const char *_X_RESTRICT_KYWD format, va_list va)
 {
     int size = vasprintf(ret, format, va);