diff --git a/src/common/boot_picobin_headers/include/boot/picobin.h b/src/common/boot_picobin_headers/include/boot/picobin.h
index 44ce9909a..40a058007 100644
--- a/src/common/boot_picobin_headers/include/boot/picobin.h
+++ b/src/common/boot_picobin_headers/include/boot/picobin.h
@@ -11,9 +11,13 @@
 #include "pico/platform.h"
 #else
 #ifndef _u
+#ifdef __ASSEMBLER__
+#define _u(x) x
+#else
 #define _u(x) x ## u
 #endif
 #endif
+#endif
 
 /** \file picobin.h
 *  \defgroup boot_picobin_headers boot_picobin_headers