diff --git a/src/util.h b/src/util.h
index 931f71c..2644e00 100644
--- a/src/util.h
+++ b/src/util.h
@@ -141,7 +141,7 @@ static SECP256K1_INLINE void *manual_alloc(void** prealloc_ptr, size_t alloc_siz
     VERIFY_CHECK(((unsigned char*)*prealloc_ptr - (unsigned char*)base) % ALIGNMENT == 0);
     VERIFY_CHECK((unsigned char*)*prealloc_ptr - (unsigned char*)base + aligned_alloc_size <= max_size);
     ret = *prealloc_ptr;
-    *((unsigned char**)prealloc_ptr) += aligned_alloc_size;
+    *prealloc_ptr = (unsigned char*)*prealloc_ptr + aligned_alloc_size;
     return ret;
 }