diff --git a/lib/libc/stdio/open_memstream.c b/lib/libc/stdio/open_memstream.c
index baa71e4a72ef..f3d1ee56cce6 100644
--- a/lib/libc/stdio/open_memstream.c
+++ b/lib/libc/stdio/open_memstream.c
@@ -31,6 +31,9 @@ __FBSDID("$FreeBSD$");
 #include "namespace.h"
 #include <assert.h>
 #include <errno.h>
+#ifdef DEBUG
+#include <inttypes.h>
+#endif
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
diff --git a/lib/libc/stdio/open_wmemstream.c b/lib/libc/stdio/open_wmemstream.c
index 299e3d87940f..458553183ac2 100644
--- a/lib/libc/stdio/open_wmemstream.c
+++ b/lib/libc/stdio/open_wmemstream.c
@@ -31,6 +31,9 @@ __FBSDID("$FreeBSD$");
 #include "namespace.h"
 #include <assert.h>
 #include <errno.h>
+#ifdef DEBUG
+#include <inttypes.h>
+#endif
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>