diff --git a/firmware/libcommon/include/assert.h b/firmware/libcommon/include/assert.h
index 22bb101d..dc6b1b52 100644
--- a/firmware/libcommon/include/assert.h
+++ b/firmware/libcommon/include/assert.h
@@ -89,7 +89,7 @@
 		/// \param condition  Condition to verify.
 		#define ASSERT(condition)  { \
 			if (!(condition)) { \
-				printf("-F- ASSERT: %s %s:%d\n\r", #condition, __BASE_FILE__, __LINE__); \
+				printf_sync("-F- ASSERT: %s %s:%d\n\r", #condition, __BASE_FILE__, __LINE__); \
 				while (1); \
 			} \
 		}
diff --git a/firmware/libosmocore/source/panic.c b/firmware/libosmocore/source/panic.c
index 74243b00..db5c26a4 100644
--- a/firmware/libosmocore/source/panic.c
+++ b/firmware/libosmocore/source/panic.c
@@ -46,7 +46,7 @@ static osmo_panic_handler_t osmo_panic_handler = (void*)0;
 __attribute__ ((format (printf, 1, 0)))
 static void osmo_panic_default(const char *fmt, va_list args)
 {
-	vfprintf(stderr, fmt, args);
+	vfprintf_sync(stderr, fmt, args);
 	osmo_generate_backtrace();
 	assert(0);
 }