diff --git a/nac3core/build.rs b/nac3core/build.rs
index 77ba9fa1..2c36a3db 100644
--- a/nac3core/build.rs
+++ b/nac3core/build.rs
@@ -26,7 +26,6 @@ fn main() {
         "-S",
         "-Wall",
         "-Wextra",
-        "-Wno-implicit-function-declaration",
         "-o",
         "-",
     ];
diff --git a/nac3core/src/codegen/irrt/irrt.c b/nac3core/src/codegen/irrt/irrt.c
index 4c091437..ba250dc9 100644
--- a/nac3core/src/codegen/irrt/irrt.c
+++ b/nac3core/src/codegen/irrt/irrt.c
@@ -104,7 +104,7 @@ int32_t __nac3_list_slice_assign_var_size(
             || MAX(src_start, src_end) < MIN(dest_start, dest_end)
         );
     if (need_alloca) {
-        uint8_t *tmp = alloca(src_arr_len * size);
+        uint8_t *tmp = __builtin_alloca(src_arr_len * size);
         __builtin_memcpy(tmp, src_arr, src_arr_len * size);
         src_arr = tmp;
     }