diff --git a/core/src/main/scala/proteus/ProtobufCodec.scala b/core/src/main/scala/proteus/ProtobufCodec.scala
index edc8122..141a2f0 100644
--- a/core/src/main/scala/proteus/ProtobufCodec.scala
+++ b/core/src/main/scala/proteus/ProtobufCodec.scala
@@ -365,12 +365,12 @@ object ProtobufCodec {
           else CodedOutputStream.computeStringSize(id, value)
         case _: PrimitiveType.Double  =>
           val value = register.asInstanceOf[Register.Double].get(registers, offset)
-          if (value == 0d && !alwaysEncode) 0
+          if (value == 0d && java.lang.Double.doubleToRawLongBits(value) == 0L && !alwaysEncode) 0
           else if (id == -1) CodedOutputStream.computeDoubleSizeNoTag(value)
           else CodedOutputStream.computeDoubleSize(id, value)
         case _: PrimitiveType.Float   =>
           val value = register.asInstanceOf[Register.Float].get(registers, offset)
-          if (value == 0f && !alwaysEncode) 0
+          if (value == 0f && java.lang.Float.floatToRawIntBits(value) == 0 && !alwaysEncode) 0
           else if (id == -1) CodedOutputStream.computeFloatSizeNoTag(value)
           else CodedOutputStream.computeFloatSize(id, value)
         case _                        => throw new ProteusException(s"Unsupported primitive type: $primitiveType")
@@ -400,12 +400,12 @@ object ProtobufCodec {
           else CodedOutputStream.computeStringSize(id, value)
         case _: PrimitiveType.Double  =>
           val value: Double = a
-          if (value == 0d && !alwaysEncode) 0
+          if (value == 0d && java.lang.Double.doubleToRawLongBits(value) == 0L && !alwaysEncode) 0
           else if (id == -1) CodedOutputStream.computeDoubleSizeNoTag(value)
           else CodedOutputStream.computeDoubleSize(id, value)
         case _: PrimitiveType.Float   =>
           val value: Float = a
-          if (value == 0f && !alwaysEncode) 0
+          if (value == 0f && java.lang.Float.floatToRawIntBits(value) == 0 && !alwaysEncode) 0
           else if (id == -1) CodedOutputStream.computeFloatSizeNoTag(value)
           else CodedOutputStream.computeFloatSize(id, value)
         case _                        => throw new ProteusException(s"Unsupported primitive type: $primitiveType")
@@ -437,12 +437,12 @@ object ProtobufCodec {
           }
         case _: PrimitiveType.Double  =>
           val value = register.asInstanceOf[Register.Double].get(registers, offset)
-          if (value != 0d || alwaysEncode) {
+          if (value != 0d || java.lang.Double.doubleToRawLongBits(value) != 0L || alwaysEncode) {
             if (id == -1) output.writeDoubleNoTag(value) else output.writeDouble(id, value)
           }
         case _: PrimitiveType.Float   =>
           val value = register.asInstanceOf[Register.Float].get(registers, offset)
-          if (value != 0f || alwaysEncode) {
+          if (value != 0f || java.lang.Float.floatToRawIntBits(value) != 0 || alwaysEncode) {
             if (id == -1) output.writeFloatNoTag(value) else output.writeFloat(id, value)
           }
         case _                        => throw new ProteusException(s"Unsupported primitive type: $primitiveType")
@@ -472,12 +472,12 @@ object ProtobufCodec {
           }
         case _: PrimitiveType.Double  =>
           val value: Double = a
-          if (value != 0d || alwaysEncode) {
+          if (value != 0d || java.lang.Double.doubleToRawLongBits(value) != 0L || alwaysEncode) {
             if (id == -1) output.writeDoubleNoTag(value) else output.writeDouble(id, value)
           }
         case _: PrimitiveType.Float   =>
           val value: Float = a
-          if (value != 0f || alwaysEncode) {
+          if (value != 0f || java.lang.Float.floatToRawIntBits(value) != 0 || alwaysEncode) {
             if (id == -1) output.writeFloatNoTag(value) else output.writeFloat(id, value)
           }
         case _                        => throw new ProteusException(s"Unsupported primitive type: $primitiveType")
diff --git a/core/src/main/scala/proteus/ProtobufDeriver.scala b/core/src/main/scala/proteus/ProtobufDeriver.scala
index c31033f..a02ab2a 100644
--- a/core/src/main/scala/proteus/ProtobufDeriver.scala
+++ b/core/src/main/scala/proteus/ProtobufDeriver.scala
@@ -271,7 +271,7 @@ case class ProtobufDeriver private (
                 getComment(field.modifiers)
               )
             case instance                                                                                                                   =>
-              val fieldId = getReservedIndex(field.modifiers) match {
+              val fieldId      = getReservedIndex(field.modifiers) match {
                 case Some(reservedIndex) => reservedIndex
                 case None                =>
                   getReservedFromIndex(field.modifiers) match {
@@ -284,12 +284,16 @@ case class ProtobufDeriver private (
                       id
                   }
               }
+              val fieldDefault = instance match {
+                case _: ProtobufCodec.Primitive[?] => getDefaultValue(using instance)
+                case _                             => field.value.getDefaultValue.getOrElse(getDefaultValue(using instance))
+              }
               builder += SimpleField(
                 name,
                 fieldId,
                 instance,
                 register,
-                field.value.getDefaultValue.getOrElse(getDefaultValue(using instance)),
+                fieldDefault,
                 getComment(field.modifiers),
                 isDeprecated(field.modifiers)
               )
diff --git a/core/src/test/scala/proteus/ProtobufCodecSpec.scala b/core/src/test/scala/proteus/ProtobufCodecSpec.scala
index 6c4e752..f798856 100644
--- a/core/src/test/scala/proteus/ProtobufCodecSpec.scala
+++ b/core/src/test/scala/proteus/ProtobufCodecSpec.scala
@@ -75,6 +75,25 @@ object ProtobufCodecSpec extends ZIOSpecDefault {
         val decoded  = codec.decode(encoded)
 
         assert(decoded)(equalTo(original))
+      },
+      test("primitive field with a non-zero default round-trips its zero value") {
+        case class WithDefault(count: Int = 5, label: String = "x") derives Schema
+        val codec = Schema[WithDefault].derive(deriver)
+
+        val original = WithDefault(0, "")
+        val decoded  = codec.decode(codec.encode(original))
+
+        assert(decoded)(equalTo(original))
+      },
+      test("negative-zero double and float fields preserve their sign bit") {
+        case class Zeros(d: Double, f: Float) derives Schema
+        val codec = Schema[Zeros].derive(deriver)
+
+        val original = Zeros(-0.0, -0.0f)
+        val decoded  = codec.decode(codec.encode(original))
+
+        assert(java.lang.Double.doubleToRawLongBits(decoded.d))(equalTo(java.lang.Double.doubleToRawLongBits(-0.0))) &&
+          assert(java.lang.Float.floatToRawIntBits(decoded.f))(equalTo(java.lang.Float.floatToRawIntBits(-0.0f)))
       }
     ),
     suite("Enum Tests")(