diff --git a/include/lefticus/tools/non_promoting_ints.hpp b/include/lefticus/tools/non_promoting_ints.hpp
index 5b07f0d..7e49ead 100644
--- a/include/lefticus/tools/non_promoting_ints.hpp
+++ b/include/lefticus/tools/non_promoting_ints.hpp
@@ -179,7 +179,7 @@ template<std::integral Type> struct int_np
 
   constexpr int_np &operator%=(const std::integral auto rhs) &noexcept
   {
-    value = static_cast<value_type>(value / rhs);
+    value = static_cast<value_type>(value % rhs);
     return *this;
   }
 
@@ -226,7 +226,7 @@ template<std::integral Type> struct int_np
 
   constexpr int_np &operator%=(const int_np rhs) &noexcept
   {
-    value = static_cast<value_type>(value / rhs.value);
+    value = static_cast<value_type>(value % rhs.value);
     return *this;
   }