diff --git a/src/include/units/quantity.h b/src/include/units/quantity.h
index ffc05be5..07f89298 100644
--- a/src/include/units/quantity.h
+++ b/src/include/units/quantity.h
@@ -203,15 +203,17 @@ public:
     return *this;
   }
 
-  constexpr quantity& operator*=(const rep& rhs)
-    requires requires(rep a, const rep b) { { a *= b } -> std::same_as<rep&>; }
+  template<typename Rep2>
+  constexpr quantity& operator*=(const Rep2& rhs)
+    requires requires(rep a, const Rep2 b) { { a *= b } -> std::same_as<rep&>; }
   {
     value_ *= rhs;
     return *this;
   }
 
-  constexpr quantity& operator/=(const rep& rhs)
-    requires requires(rep a, const rep b) { { a /= b } -> std::same_as<rep&>; }
+  template<typename Rep2>
+  constexpr quantity& operator/=(const Rep2& rhs)
+    requires requires(rep a, const Rep2 b) { { a /= b } -> std::same_as<rep&>; }
   {
     value_ /= rhs;
     return *this;
diff --git a/test/unit_test/static/CMakeLists.txt b/test/unit_test/static/CMakeLists.txt
index d44aa529..804544f4 100644
--- a/test/unit_test/static/CMakeLists.txt
+++ b/test/unit_test/static/CMakeLists.txt
@@ -51,3 +51,5 @@ target_link_libraries(unit_tests_static
     PRIVATE
         mp::units
 )
+
+set_source_files_properties(quantity_test.cpp PROPERTIES COMPILE_FLAGS -Wno-conversion)
diff --git a/test/unit_test/static/quantity_test.cpp b/test/unit_test/static/quantity_test.cpp
index 5cd3c2f8..76d87e08 100644
--- a/test/unit_test/static/quantity_test.cpp
+++ b/test/unit_test/static/quantity_test.cpp
@@ -283,6 +283,11 @@ static_assert((2.5_q_m *= 3).count() == 7.5);
 static_assert((7.5_q_m /= 3).count() == 2.5);
 static_assert((3500_q_m %= 1_q_km).count() == 500);
 
+// next two lines trigger the gcc 'Wconversion' warning
+// (warning disabled in CMake for this file)
+static_assert((22_q_m *= 33.33).count() == 733);
+static_assert((22_q_m /= 3.33).count() == 6);
+
 template<typename Metre>
 concept invalid_compound_assignments = requires() {
   // truncating not allowed