diff --git a/core/src/test/scala/com/avsystem/commons/serialization/IgnoreTransientDefaultMarkerTest.scala b/core/src/test/scala/com/avsystem/commons/serialization/IgnoreTransientDefaultMarkerTest.scala
index 8032a8b0a..30fe2c0b2 100644
--- a/core/src/test/scala/com/avsystem/commons/serialization/IgnoreTransientDefaultMarkerTest.scala
+++ b/core/src/test/scala/com/avsystem/commons/serialization/IgnoreTransientDefaultMarkerTest.scala
@@ -11,6 +11,12 @@ object IgnoreTransientDefaultMarkerTest {
     @transientDefault defaultObj: HasDefaults = HasDefaults(),
   )
   object NestedHasDefaults extends HasGenCodec[NestedHasDefaults]
+
+  final case class HasOptParam(
+    @transientDefault flag: Boolean = false,
+    @optionalParam str: Opt[String] = Opt.Empty,
+  )
+  object HasOptParam extends HasGenCodec[HasOptParam]
 }
 
 class IgnoreTransientDefaultMarkerTest extends AbstractCodecTest {
@@ -24,16 +30,31 @@ class IgnoreTransientDefaultMarkerTest extends AbstractCodecTest {
     result
   }
 
-  def createInput(raw: Any): Input = new SimpleValueInput(raw)
+  def createInput(raw: Any): Input =
+    CustomMarkersInputWrapper(new SimpleValueInput(raw), IgnoreTransientDefaultMarker)
 
-  test("case class with default values") {
+  test("write case class with default values") {
     testWrite(HasDefaults(str = "lol"), Map("str" -> "lol", "int" -> 42))
     testWrite(HasDefaults(43, "lol"), Map("int" -> 43, "str" -> "lol"))
     testWrite(HasDefaults(str = null), Map("str" -> null, "int" -> 42))
     testWrite(HasDefaults(str = "dafuq"), Map("str" -> "dafuq", "int" -> 42))
   }
 
-  test("nested case class with default values") {
+  test("read case class with default values") {
+    testRead(Map("str" -> "lol", "int" -> 42), HasDefaults(str = "lol", int = 42))
+    testRead(Map("str" -> "lol"), HasDefaults(str = "lol", int = 42))
+    testRead(Map("int" -> 43, "str" -> "lol"), HasDefaults(int = 43, str = "lol"))
+    testRead(Map("str" -> null, "int" -> 42), HasDefaults(str = null, int = 42))
+    testRead(Map("str" -> null), HasDefaults(str = null, int = 42))
+    testRead(Map(), HasDefaults(str = "dafuq", int = 42))
+  }
+
+  test("write case class with opt values") {
+    testWrite(HasOptParam(str = "lol".opt), Map("flag" -> false, "str" -> "lol"))
+    testWrite(HasOptParam(), Map("flag" -> false))
+  }
+
+  test("write nested case class with default values") {
     testWrite(
       value = NestedHasDefaults(
         flag = false,
diff --git a/macros/src/main/scala/com/avsystem/commons/macros/serialization/GenCodecMacros.scala b/macros/src/main/scala/com/avsystem/commons/macros/serialization/GenCodecMacros.scala
index a186d3aff..534a58703 100644
--- a/macros/src/main/scala/com/avsystem/commons/macros/serialization/GenCodecMacros.scala
+++ b/macros/src/main/scala/com/avsystem/commons/macros/serialization/GenCodecMacros.scala
@@ -172,24 +172,48 @@ class GenCodecMacros(ctx: blackbox.Context) extends CodecMacroCommons(ctx) with
       }
     }
 
-    def writeField(p: ApplyParam, value: Tree): Tree = {
+    def doWriteField(p: ApplyParam, value: Tree, transientValue: Option[Tree]): Tree = {
+      val writeArgs = q"output" :: q"${p.idx}" :: value :: transientValue.toList
+      val writeTargs = if (isOptimizedPrimitive(p)) Nil else List(p.valueType)
+      q"writeField[..$writeTargs](..$writeArgs)"
+    }
+
+    def writeFieldNoTransientDefault(p: ApplyParam, value: Tree): Tree = {
+      val transientValue = p.optionLike.map(ol => q"${ol.reference(Nil)}.none")
+      doWriteField(p, value, transientValue)
+    }
+
+    def writeFieldTransientDefaultPossible(p: ApplyParam, value: Tree): Tree = {
       val transientValue =
         if (isTransientDefault(p)) Some(p.defaultValue)
         else p.optionLike.map(ol => q"${ol.reference(Nil)}.none")
-
-      val writeArgsNoTransient = q"output" :: q"${p.idx}" :: List(value)
-      val writeArgs = writeArgsNoTransient ::: transientValue.toList
-      val writeTargs = if (isOptimizedPrimitive(p)) Nil else List(p.valueType)
-      q"""
-        if (ignoreTransientDefault)
-          writeField[..$writeTargs](..$writeArgsNoTransient)
-        else
-          writeField[..$writeTargs](..$writeArgs)
-       """
+      doWriteField(p, value, transientValue)
     }
 
+    def writeField(p: ApplyParam, value: Tree, ignoreTransientDefault: Tree): Tree =
+      if (isTransientDefault(p))
+        q"""
+          if ($ignoreTransientDefault) ${writeFieldNoTransientDefault(p, value)}
+          else ${writeFieldTransientDefaultPossible(p, value)}
+         """
+      else
+        writeFieldNoTransientDefault(p, value)
+
     def ignoreTransientDefaultCheck: Tree =
-      q"val ignoreTransientDefault = output.customEvent($SerializationPkg.IgnoreTransientDefaultMarker, ())"
+      q"output.customEvent($SerializationPkg.IgnoreTransientDefaultMarker, ())"
+
+    // when params size is 1
+    def writeSingle(p: ApplyParam, value: Tree): Tree =
+      writeField(p, value, ignoreTransientDefaultCheck)
+
+    // when params size is greater than 1
+    def writeMultiple(value: ApplyParam => Tree): Tree =
+      if (anyParamHasTransientDefault) {
+        q"""
+          val ignoreTransientDefault = $ignoreTransientDefaultCheck
+          ..${params.map(p => writeField(p, value(p), q"ignoreTransientDefault"))}
+         """
+      } else q"..${params.map(p => writeFieldNoTransientDefault(p, value(p)))}"
 
     def writeFields: Tree = params match {
       case Nil =>
@@ -203,37 +227,30 @@ class GenCodecMacros(ctx: blackbox.Context) extends CodecMacroCommons(ctx) with
            """
       case List(p: ApplyParam) =>
         if (canUseFields)
-          q"""
-            $ignoreTransientDefaultCheck
-            ${writeField(p, q"value.${p.sym.name}")}
-           """
+          q"${writeSingle(p, q"value.${p.sym.name}")}"
         else
           q"""
             val unapplyRes = $companion.$unapply[..${dtpe.typeArgs}](value)
             if (unapplyRes.isEmpty) unapplyFailed
-            else {
-              $ignoreTransientDefaultCheck
-              ${writeField(p, q"unapplyRes.get")}
-            }
+            else ${writeSingle(p, q"unapplyRes.get")}
            """
       case _ =>
         if (canUseFields)
-          q"""
-            $ignoreTransientDefaultCheck
-            ..${params.map(p => writeField(p, q"value.${p.sym.name}"))}
-           """
+          q"${writeMultiple(p => q"value.${p.sym.name}")}"
         else
           q"""
             val unapplyRes = $companion.$unapply[..${dtpe.typeArgs}](value)
             if (unapplyRes.isEmpty) unapplyFailed
             else {
               val t = unapplyRes.get
-              $ignoreTransientDefaultCheck
-              ..${params.map(p => writeField(p, q"t.${tupleGet(p.idx)}"))}
+              ${writeMultiple(p => q"t.${tupleGet(p.idx)}")}
             }
            """
     }
 
+    def anyParamHasTransientDefault: Boolean =
+      params.exists(isTransientDefault)
+
     def mayBeTransient(p: ApplyParam): Boolean =
       p.optionLike.nonEmpty || isTransientDefault(p)