diff --git a/libc/assert.c b/libc/assert.c
index b50291bc..e530124c 100644
--- a/libc/assert.c
+++ b/libc/assert.c
@@ -1,4 +1,6 @@
+#include <stdio.h>
 
 void __assert_func(const char * file, int line, const char * func, const char * failedexpr) {
+ fprintf(stderr, "Assertion failed in %s:%d (%s): %s\n", file, line, func, failedexpr);
  // void
 }