diff --git a/src/system.rs b/src/system.rs
index a9fb3b70..37ea186f 100644
--- a/src/system.rs
+++ b/src/system.rs
@@ -553,6 +553,21 @@ macro_rules! system {
                     }
                 }
 
+                impl<D, Ul, Ur, V> $crate::lib::ops::$MulDivAssignTrait<Quantity<DimensionOne, Ur, V>> for Quantity<D, Ul, V>
+                where
+                    D: Dimension + ?Sized,
+                    D::Kind: $crate::marker::$MulDivAssignTrait,
+                    Ul: Units<V> + ?Sized,
+                    Ur: Units<V> + ?Sized,
+                    V: $crate::num::Num + $crate::Conversion<V>
+                        + $crate::lib::ops::$MulDivAssignTrait<Quantity<DimensionOne, Ur, V>>,
+                {
+                    #[inline(always)]
+                    fn $muldivassign_fun(&mut self, rhs: Quantity<DimensionOne, Ur, V>) {
+                        self.value $muldivassign_op rhs;
+                    }
+                }
+
                 #[doc(hidden)]
                 mod $Mod {
                     storage_types! {
diff --git a/src/tests/impl_ops.rs b/src/tests/impl_ops.rs
index 56b3f981..043bd1e7 100644
--- a/src/tests/impl_ops.rs
+++ b/src/tests/impl_ops.rs
@@ -123,10 +123,10 @@ mod vv {
         test!(div_ratio_right          m(6.)   /  ratio(2.),        m(3.)); //      6    c.f. BBB below
         test!(mul_ratio_right_p        m(4.)   *   pct(50.),        m(2.)); //      6    c.f. CCC below
         test!(div_ratio_right_p        m(4.)   /   pct(50.),        m(8.)); //      6    c.f. DDD below
-     // test!(mul_assign_ratio    [    m(4.) ] *= ratio(2.),        m(8.)); //  ERR      c.f. AAA above
-     // test!(div_assign_ratio    [    m(6.) ] /= ratio(2.),        m(3.)); //  ERR      c.f. BBB above
-     // test!(mul_assign_ratio_p  [    m(4.) ] *=  pct(50.),        m(4.)); //  ERR      c.f. CCC above
-     // test!(div_assign_ratio_p  [    m(4.) ] /=  pct(50.),        m(8.)); //  ERR      c.f. DDD above
+        test!(mul_assign_ratio    [    m(4.) ] *= ratio(2.),        m(8.)); //  ERR      c.f. AAA above
+        test!(div_assign_ratio    [    m(6.) ] /= ratio(2.),        m(3.)); //  ERR      c.f. BBB above
+        test!(mul_assign_ratio_p  [    m(4.) ] *=  pct(50.),        m(4.)); //  ERR      c.f. CCC above
+        test!(div_assign_ratio_p  [    m(4.) ] /=  pct(50.),        m(8.)); //  ERR      c.f. DDD above
         test!(mul_bare_right           m(4.)   *        2. ,        m(8.)); //       7
         test!(div_bare_right           m(6.)   /        2. ,        m(3.)); //       7
         test!(mul_assign_bare     [    m(2.) ] *=       3. ,        m(6.)); //        8