diff --git a/lib/libc/minimal/io.c b/lib/libc/minimal/io.c
index 0badb95..6754a46 100644
--- a/lib/libc/minimal/io.c
+++ b/lib/libc/minimal/io.c
@@ -223,7 +223,7 @@ char *strchr(const char *s, int c)
 
 static void pos_libc_putc_stdout(char c)
 {
-    *(uint32_t *)(long)(ARCHI_STDOUT_ADDR + STDOUT_PUTC_OFFSET + (hal_core_id()<<3) + (hal_cluster_id()<<7)) = c;
+    *(volatile uint32_t *)(long)(ARCHI_STDOUT_ADDR + STDOUT_PUTC_OFFSET + (hal_core_id()<<3) + (hal_cluster_id()<<7)) = c;
 }