diff --git a/lib/Case.vala b/lib/Case.vala
index 82afdd6..ffe54cc 100644
--- a/lib/Case.vala
+++ b/lib/Case.vala
@@ -59,7 +59,8 @@ namespace ChCase {
                 case Case.SENTENCE:
                     return "sentence";
                 default:
-                    assert_not_reached ();
+                    warning ("Invalid Case: %d", this);
+                    return "";
             }
         }
     }
diff --git a/lib/Converter.vala b/lib/Converter.vala
index 86250e3..d9551c0 100644
--- a/lib/Converter.vala
+++ b/lib/Converter.vala
@@ -266,7 +266,8 @@ namespace ChCase {
                     regex_pattern = new PatternType.Sentence (result_case);
                     break;
                 default:
-                    assert_not_reached ();
+                    warning ("Invalid Case: %d", source_case);
+                    return result;
             }
 
             try {