diff --git a/compiler-plugin/src/main/kotlin/community/flock/kmapper/compiler/fir/KMapperFirMappingChecker.kt b/compiler-plugin/src/main/kotlin/community/flock/kmapper/compiler/fir/KMapperFirMappingChecker.kt
index 558a0b1..e39244f 100644
--- a/compiler-plugin/src/main/kotlin/community/flock/kmapper/compiler/fir/KMapperFirMappingChecker.kt
+++ b/compiler-plugin/src/main/kotlin/community/flock/kmapper/compiler/fir/KMapperFirMappingChecker.kt
@@ -20,6 +20,7 @@ import org.jetbrains.kotlin.fir.declarations.utils.isEnumClass
 import org.jetbrains.kotlin.fir.expressions.FirAnonymousFunctionExpression
 import org.jetbrains.kotlin.fir.expressions.FirCall
 import org.jetbrains.kotlin.fir.expressions.FirFunctionCall
+import org.jetbrains.kotlin.fir.expressions.FirQualifiedAccessExpression
 import org.jetbrains.kotlin.fir.expressions.arguments
 import org.jetbrains.kotlin.fir.expressions.explicitReceiver
 import org.jetbrains.kotlin.fir.expressions.toReference
@@ -96,10 +97,13 @@ class KMapperFirMappingChecker(val collector: MessageCollector, private val sess
                                 val propSymbol = call.explicitReceiver
                                     ?.toReference(session)
                                     ?.toResolvedPropertySymbol()
+                                val propName = propSymbol?.name
+                                    ?: (call.explicitReceiver as? FirQualifiedAccessExpression)
+                                        ?.calleeReference?.let { it as? FirNamedReference }?.name
                                 val valueExpr = call.arguments.firstOrNull()
-                                if (propSymbol != null && valueExpr != null) {
+                                if (propName != null && valueExpr != null) {
                                     Field(
-                                        name = propSymbol.name,
+                                        name = propName,
                                         type = valueExpr.resolvedType,
                                         hasDefaultValue = false,
                                         fields = valueExpr.resolvedType.resolveConstructorFields()
@@ -110,9 +114,12 @@ class KMapperFirMappingChecker(val collector: MessageCollector, private val sess
                                 val propSymbol = call.extensionReceiver
                                     ?.toReference(session)
                                     ?.toResolvedPropertySymbol()
-                                if (propSymbol != null) {
+                                val propName = propSymbol?.name
+                                    ?: (call.extensionReceiver as? FirQualifiedAccessExpression)
+                                        ?.calleeReference?.let { it as? FirNamedReference }?.name
+                                if (propName != null) {
                                     // Find the matching toField to include its type info
-                                    toFields.find { it.name == propSymbol.name }
+                                    toFields.find { it.name == propName }
                                 } else null
                             }
                             else -> null
diff --git a/test-integration/src/test/kotlin/community/flock/kmapper/SerializableTest.kt b/test-integration/src/test/kotlin/community/flock/kmapper/SerializableTest.kt
index 28edc48..52c38f7 100644
--- a/test-integration/src/test/kotlin/community/flock/kmapper/SerializableTest.kt
+++ b/test-integration/src/test/kotlin/community/flock/kmapper/SerializableTest.kt
@@ -111,6 +111,65 @@ class SerializableTest {
             }
     }
 
+    @Test
+    fun shouldCompile_explicitMappingWithSerializableTargetInSeparateFile() {
+        IntegrationTest(options)
+            .file("Dto.kt") {
+                $$"""
+                |package sample
+                |
+                |import kotlinx.serialization.Serializable
+                |import kotlinx.serialization.SerialName
+                |
+                |@Serializable
+                |@SerialName("RunAnnotationDataDto")
+                |data class RunAnnotationDataDto(
+                |    val runId: String,
+                |    val displayId: String,
+                |    val inputHash: String,
+                |    val outputJson: String,
+                |)
+                |
+                """.trimMargin()
+            }
+            .file("App.kt") {
+                $$"""
+                |package sample
+                |
+                |import community.flock.kmapper.mapper
+                |
+                |data class RunAnnotationData(
+                |    val runId: String,
+                |    val sequenceNumber: Int,
+                |    val inputHash: String,
+                |    val outputJson: String,
+                |)
+                |
+                |fun RunAnnotationData.toDto(): RunAnnotationDataDto = mapper {
+                |    displayId = it.sequenceNumber.toString()
+                |}
+                |
+                |fun main() {
+                |    val data = RunAnnotationData(
+                |        runId = "run-1",
+                |        sequenceNumber = 42,
+                |        inputHash = "abc123",
+                |        outputJson = "{}"
+                |    )
+                |    val dto = data.toDto()
+                |    println(dto)
+                |}
+                |
+                """.trimMargin()
+            }
+            .compileSuccess { output ->
+                assertTrue(
+                    output.contains("RunAnnotationDataDto(runId=run-1, displayId=42, inputHash=abc123, outputJson={})"),
+                    "Expected RunAnnotationDataDto(runId=run-1, displayId=42, inputHash=abc123, outputJson={}) in output"
+                )
+            }
+    }
+
     @Test
     fun shouldCompile_allFieldsAutoMappedWithSerializable() {
         IntegrationTest(options)