diff --git a/class/Tasks/TruthTableTask.php b/class/Tasks/TruthTableTask.php
index 43c3256..75676fc 100644
--- a/class/Tasks/TruthTableTask.php
+++ b/class/Tasks/TruthTableTask.php
@@ -55,12 +55,21 @@ class TruthTableTask extends PicturedTask
         return $this->lf;
     }
 
+    public static function sanitizeIndices(array $a): array {
+        $r = [];
+        $i = 0;
+        foreach ($a as $v) {
+            $r[$i++] = $v;
+        }
+        return $r;
+    }
+
     public function generateRandomFunction(array $input_vars, int $min_depth, int $max_depth): void {
-        $this->lf = LogicFunction::genRandom($input_vars, $min_depth, $max_depth);
+        $this->lf = LogicFunction::genRandom(self::sanitizeIndices($input_vars), $min_depth, $max_depth);
     }
 
     public function generateRandomDF(array $input_vars): void {
-        $this->lf = LogicFunction::genRandomDF($input_vars);
+        $this->lf = LogicFunction::genRandomDF(self::sanitizeIndices($input_vars));
     }
 
     public function getFunctionAsDNF(): string {
@@ -72,7 +81,7 @@ class TruthTableTask extends PicturedTask
     }
 
     public function setLogicFunctionExpr(string $expr, array $input_vars = []): void {
-        $this->lf = new LogicFunction($expr, $input_vars);
+        $this->lf = new LogicFunction($expr, self::sanitizeIndices($input_vars));
     }
 
     public function getLogicFunctionExpr(string $fmt = "verilog_bitwise"): string {