diff --git a/tfshark.c b/tfshark.c
index 5f53c5bce7..c8f543376d 100644
--- a/tfshark.c
+++ b/tfshark.c
@@ -616,6 +616,14 @@ main(int argc, char *argv[])
       case PREFS_SET_OK:
         break;
 
+      case PREFS_SET_SYNTAX_ERR:
+        cmdarg_err("Invalid -o flag \"%s\"%s%s", ws_optarg,
+            errmsg ? ": " : "", errmsg ? errmsg : "");
+        g_free(errmsg);
+        exit_status = INVALID_OPTION;
+        goto clean_exit;
+        break;
+
       case PREFS_SET_NO_SUCH_PREF:
         cmdarg_err("-o flag \"%s\" specifies unknown preference", ws_optarg);
         exit_status = INVALID_OPTION;