diff --git a/Source/m_misc2.c b/Source/m_misc2.c
index eb11afba..35e973e0 100644
--- a/Source/m_misc2.c
+++ b/Source/m_misc2.c
@@ -419,7 +419,7 @@ char *M_StringJoin(const char *s, ...)
 #endif
 
 // Safe, portable vsnprintf().
-static int M_vsnprintf(char *buf, size_t buf_len, const char *s, va_list args)
+static int PRINTF_ATTR(3, 0) M_vsnprintf(char *buf, size_t buf_len, const char *s, va_list args)
 {
     int result;