diff --git a/jsvn b/jsvn
index 6c034eb..6ee2a17 100755
--- a/jsvn
+++ b/jsvn
@@ -1138,6 +1138,9 @@ def log_h(argv, svn, out, config):
                 if match != target:
                     return False
         return True
+    if pretty not in ("default", "oneline"):
+        sys.stderr.write("Error: unknown --pretty option: '%s'\n" % pretty)
+        return RET_ERR
     pout = Popen([svn] + argv, stdout=PIPE).stdout
     while True:
         le = LogEntry(pout)