diff --git a/src/exec.c b/src/exec.c
index 9f16165..8fd887b 100644
--- a/src/exec.c
+++ b/src/exec.c
@@ -18,6 +18,13 @@ AST* exec_start(AST* ast) {
 
     HTab* global = htab_init();
 
+    for (int i = 0; i < NBUILTIN_FNS; i++)
+        htab_ins(
+            global, builtin_fns_names[i],
+            ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_fns[i]))
+        );
+
+    /*
     htab_ins(
         global, "sum", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_sum))
     );
@@ -32,7 +39,7 @@ AST* exec_start(AST* ast) {
 
     htab_ins(
         global, "div", ast_init(AST_TYPE_BIF, ast_bif_data_init(builtin_div))
-    );
+        );*/
 
     // Push global namespace to `scope`.
     stack_push(scope, global);
diff --git a/src/include/builtin.h b/src/include/builtin.h
index c4c58f3..e2f1363 100644
--- a/src/include/builtin.h
+++ b/src/include/builtin.h
@@ -15,9 +15,14 @@ AST* builtin_mul(size_t argc, AST** argv);
 // Divide nums.
 AST* builtin_div(size_t argc, AST** argv);
 
+#define NBUILTIN_FNS 4
 // The list of built-in functions.
-static AST* (*builtin_fns[])(size_t argc, AST** argv) = {
+static AST* (*builtin_fns[NBUILTIN_FNS])(size_t argc, AST** argv) = {
     builtin_sum, builtin_sub, builtin_mul, builtin_div
 };
 
+static char* builtin_fns_names[NBUILTIN_FNS] = {
+    "sum", "sub", "mul", "div"
+};
+
 #endif