diff --git a/contrib/credential/osxkeychain/git-credential-osxkeychain.c b/contrib/credential/osxkeychain/git-credential-osxkeychain.c
index 6a40917b1e..b5346005a4 100644
--- a/contrib/credential/osxkeychain/git-credential-osxkeychain.c
+++ b/contrib/credential/osxkeychain/git-credential-osxkeychain.c
@@ -140,7 +140,7 @@ static void find_username_in_item(CFDictionaryRef item)
 				username_buf,
 				buffer_len,
 				ENCODING)) {
-		write_item("username", username_buf, buffer_len - 1);
+		write_item("username", username_buf, strlen(username_buf));
 	}
 	free(username_buf);
 }