diff --git a/test/test_hex.c b/test/test_hex.c
index d7a111b..a3c7bc4 100644
--- a/test/test_hex.c
+++ b/test/test_hex.c
@@ -15,7 +15,7 @@ END_TEST
 
 START_TEST (test_uc_hex_encode_2)
     uint8_t binary[] = {127, 128, 129};
-    char hex[4] = "";
+    char hex[sizeof binary * 2 + 1] = "";
 
     uc_hex_encode(binary, sizeof binary, hex);
 
@@ -25,7 +25,7 @@ END_TEST
 
 START_TEST (test_uc_hex_encode_3)
     uint8_t binary[] = {0, 1, 9, 11};
-    char hex[5] = "";
+    char hex[sizeof binary * 2 + 1] = "";
 
     uc_hex_encode(binary, sizeof binary, hex);