diff --git a/src/message_test.c b/src/message_test.c
index 85a29b4..88335de 100644
--- a/src/message_test.c
+++ b/src/message_test.c
@@ -49,6 +49,15 @@
     char_u  *buf; /*allocated every time to find uninit errors */
     char_u  *s;
 
+    // Should not write anything to destination if buflen is 0.
+    trunc_string((char_u *)"", NULL, 1, 0);
+
+    // Truncating an empty string does nothing.
+    buf = alloc(1);
+    trunc_string((char_u *)"", buf, 1, 1);
+    assert(buf[0] == NUL);
+    vim_free(buf);
+
     // in place
     buf = alloc(40);
     STRCPY(buf, "text");