diff --git a/test/tests/testunity.c b/test/tests/testunity.c
index 9fae64e..77eeb21 100644
--- a/test/tests/testunity.c
+++ b/test/tests/testunity.c
@@ -8,6 +8,8 @@
 #include "unity.h"
 #include <string.h>
 
+int putcharSpy(int c);
+
 // Dividing by these constants produces +/- infinity.
 // The rationale is given in UnityAssertFloatIsInf's body.
 #ifndef UNITY_EXCLUDE_FLOAT