diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..5067f82
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+.dub
+*.exe
diff --git a/source/runner.d b/source/runner.d
index 67eb97f..7a46105 100644
--- a/source/runner.d
+++ b/source/runner.d
@@ -203,7 +203,8 @@ class Runner
 			return 0;
 		}
 
-		assert (false);
+		throw new Exception ("call of non-existing function: " ~
+		    call.name);
 	}
 
 	long evalExpression (Expression e)