diff --git a/src/secp256k1.c b/src/secp256k1.c
index 866c2e4..6a2e63c 100644
--- a/src/secp256k1.c
+++ b/src/secp256k1.c
@@ -34,6 +34,8 @@
 } while(0)
 
 #ifndef USE_EXTERNAL_DEFAULT_CALLBACKS
+#include <stdlib.h>
+#include <stdio.h>
 static void default_illegal_callback_fn(const char* str, void* data) {
     (void)data;
     fprintf(stderr, "[libsecp256k1] illegal argument: %s\n", str);