diff --git a/src/public/cast.c b/src/public/cast.c
index f4aa4e63..fede7ccc 100644
--- a/src/public/cast.c
+++ b/src/public/cast.c
@@ -5,10 +5,12 @@
 #include "pocketpy/interpreter/vm.h"
 
 int64_t py_toint(const py_Ref self){
+    assert(self->type == tp_int);
     return self->_i64;
 }
 
 double py_tofloat(const py_Ref self){
+    assert(self->type == tp_float);
     return self->_f64;
 }
 
@@ -29,15 +31,18 @@ bool py_castfloat(const py_Ref self, double* out){
 }
 
 bool py_tobool(const py_Ref self){
+    assert(self->type == tp_bool);
     return self->extra;
 }
 
 const char* py_tostr(const py_Ref self){
+    assert(self->type == tp_str);
     py_Str* ud = PyObject__value(self->_obj);
     return py_Str__data(ud);
 }
 
 const char* py_tostrn(const py_Ref self, int* out){
+    assert(self->type == tp_str);
     py_Str* ud = PyObject__value(self->_obj);
     *out = ud->size;
     return py_Str__data(ud);
diff --git a/src2/main.c b/src2/main.c
index ea1e1e15..06343b84 100644
--- a/src2/main.c
+++ b/src2/main.c
@@ -25,7 +25,7 @@ int main(int argc, char** argv) {
 #endif
 
     py_initialize();
-    const char* source = "[1+2, 'a']";
+    const char* source = "[1/2, 'a']";
 
     py_Ref r0 = py_reg(0);
     if(py_eval(source, r0)){
@@ -35,9 +35,9 @@ int main(int argc, char** argv) {
         // handle the result
         py_Ref _0 = py_list__getitem(r0, 0);
         py_Ref _1 = py_list__getitem(r0, 1);
-        int _L0 = py_toint(_0);
+        float _L0 = py_tofloat(_0);
         const char* _L1 = py_tostr(_1);
-        printf("%d, %s\n", _L0, _L1);
+        printf("%f, %s\n", _L0, _L1);
     }
 
     py_finalize();