diff --git a/src/util/u_debug.c b/src/util/u_debug.c
index 7282179c122..f14a260622c 100644
--- a/src/util/u_debug.c
+++ b/src/util/u_debug.c
@@ -30,6 +30,7 @@
 #include "util/u_debug.h"
 #include "util/u_string.h"
 #include "util/u_math.h"
+#include "c11/threads.h"
 #include <inttypes.h>
 
 #include <stdio.h>
@@ -378,8 +379,8 @@ debug_dump_enum(const struct debug_named_value *names,
 const char *
 debug_dump_flags(const struct debug_named_value *names, uint64_t value)
 {
-   static char output[4096];
-   static char rest[256];
+   static thread_local char output[4096];
+   static thread_local char rest[256];
    int first = 1;
 
    output[0] = '\0';