diff --git a/sources/zweic/Parser.scala b/sources/zweic/Parser.scala
index af38b8e..1b9081f 100755
--- a/sources/zweic/Parser.scala
+++ b/sources/zweic/Parser.scala
@@ -383,7 +383,7 @@
 	case DIV => nextToken; return null;
 	case MOD => nextToken; return null;
 	case AND => nextToken; return null;
-	case _ => error("illegal start of expression"); return null;
+	case _ => error("'*', '/', '%' or '&&' token"); return null;
   }
 
   /**
@@ -392,7 +392,7 @@
   private def negateOp(): Tree = token match {
 	case SUB => nextToken; return null;
 	case NOT => nextToken; return null;
-	case _ => error("illegal start of expression"); return null;
+	case _ => error("'-' or '!' token"); return null;
   }
 
   /**
@@ -402,7 +402,7 @@
 	case ADD => nextToken; return null;
 	case SUB => nextToken; return null;
 	case OR => nextToken; return null;
-	case _ => error("illegal start of expression"); return null;
+	case _ => error("'+', '-' or '||' token"); return null;
   }
 
 
@@ -416,7 +416,7 @@
 	case GT => nextToken; return null;
 	case LE => nextToken; return null;
 	case GE => nextToken; return null;
-	case _ => error("illegal start of expression"); return null;
+	case _ => error("comparison operator ('==', '!', '<', '>', '<=', '>=')"); return null;
   }
 
 }