diff --git a/src/common/tusb_common.h b/src/common/tusb_common.h
index 0d4082c031..09bf358aa7 100644
--- a/src/common/tusb_common.h
+++ b/src/common/tusb_common.h
@@ -69,6 +69,7 @@
 #include <stddef.h>
 #include <string.h>
 #include <stdio.h>
+#include <stdarg.h>
 
 // Tinyusb Common Headers
 #include "tusb_option.h"
diff --git a/src/common/tusb_debug.h b/src/common/tusb_debug.h
index 2e9f1d9cdc..9879646e12 100644
--- a/src/common/tusb_debug.h
+++ b/src/common/tusb_debug.h
@@ -50,12 +50,14 @@ extern char const* const tu_str_xfer_result[];
 #endif
 
 void tu_print_mem(void const *buf, uint32_t count, uint8_t indent);
+int tu_printf_r(const char *format, ...);
 
 #ifdef CFG_TUSB_DEBUG_PRINTF
+  // External debug print function, must be ISR-safe
   extern int CFG_TUSB_DEBUG_PRINTF(const char *format, ...);
   #define tu_printf    CFG_TUSB_DEBUG_PRINTF
 #else
-  #define tu_printf    printf
+  #define tu_printf    tu_printf_r
 #endif
 
 static inline void tu_print_buf(uint8_t const* buf, uint32_t bufsize) {
diff --git a/src/tusb.c b/src/tusb.c
index 0092267a19..88836045f2 100644
--- a/src/tusb.c
+++ b/src/tusb.c
@@ -452,6 +452,22 @@ void tu_print_mem(void const* buf, uint32_t count, uint8_t indent) {
   dump_str_line(buf8 - nback, nback);
 }
 
+int tu_printf_r(const char *format, ...)
+{
+  // Simple re-entrancy lock, not safe for multi-core MCU
+  static volatile bool lock = false;
+  if (lock) {
+    return -1;
+  }
+  lock = true;
+  va_list args;
+  va_start(args, format);
+  int ret = vprintf(format, args);
+  va_end(args);
+  lock = false;
+  return ret;
+}
+
 #endif
 
 #endif // host or device enabled