diff --git a/sha1_file.c b/sha1_file.c
index 6011473..d451a94 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -81,6 +81,8 @@
 		*buf++ = hex[val >> 4];
 		*buf++ = hex[val & 0xf];
 	}
+	*buf = '\0';
+
 	return buffer;
 }