diff --git a/compiler-plugin/src/main/kotlin/tech/mappie/util/Ir.kt b/compiler-plugin/src/main/kotlin/tech/mappie/util/Ir.kt
index b0e60970..91b15e7c 100644
--- a/compiler-plugin/src/main/kotlin/tech/mappie/util/Ir.kt
+++ b/compiler-plugin/src/main/kotlin/tech/mappie/util/Ir.kt
@@ -25,7 +25,16 @@ internal fun IrClass.allSuperTypes(): List<IrType> =
     this.superTypes + this.superTypes.flatMap { it.erasedUpperBound.allSuperTypes() }
 
 fun IrType.isAssignableFrom(other: IrType): Boolean =
-    isSubtypeOf(other, IrTypeSystemContextImpl(context.irBuiltIns)) && (isNullable() || !other.isNullable())
+    other.isSubtypeOf(this, IrTypeSystemContextImpl(context.irBuiltIns)) || isIntegerAssignableFrom(other)
+
+fun IrType.isIntegerAssignableFrom(other: IrType): Boolean =
+    when (other) {
+        context.irBuiltIns.byteType -> this in listOf(context.irBuiltIns.byteType)
+        context.irBuiltIns.shortType -> this in listOf(context.irBuiltIns.byteType, context.irBuiltIns.shortType)
+        context.irBuiltIns.intType -> this in listOf(context.irBuiltIns.byteType, context.irBuiltIns.shortType, context.irBuiltIns.intType)
+        context.irBuiltIns.longType -> this in listOf(context.irBuiltIns.byteType, context.irBuiltIns.shortType, context.irBuiltIns.intType, context.irBuiltIns.longType)
+        else -> false
+    }
 
 fun getterName(name: Name) =
     getterName(name.asString())
diff --git a/mappie-api/build.gradle.kts b/mappie-api/build.gradle.kts
index 2f1e283a..c564783b 100644
--- a/mappie-api/build.gradle.kts
+++ b/mappie-api/build.gradle.kts
@@ -1,5 +1,3 @@
-import org.jetbrains.dokka.gradle.DokkaTask
-
 plugins {
     alias(libs.plugins.kotlin.multiplatform)
     alias(libs.plugins.dokka)
diff --git a/testing/src/main/kotlin/testing/IdentityMapper.kt b/testing/src/main/kotlin/testing/IntIdentityMapper.kt
similarity index 67%
rename from testing/src/main/kotlin/testing/IdentityMapper.kt
rename to testing/src/main/kotlin/testing/IntIdentityMapper.kt
index 4b0b4083..02bd371a 100644
--- a/testing/src/main/kotlin/testing/IdentityMapper.kt
+++ b/testing/src/main/kotlin/testing/IntIdentityMapper.kt
@@ -2,6 +2,6 @@ package testing
 
 import tech.mappie.api.Mappie
 
-object IdentityMapper : Mappie<Int, Int>() {
+object IntIdentityMapper : Mappie<Int, Int>() {
     override fun map(from: Int): Int = mapping()
 }
\ No newline at end of file
diff --git a/testing/src/main/kotlin/testing/IntToLongMapper.kt b/testing/src/main/kotlin/testing/IntToLongMapper.kt
new file mode 100644
index 00000000..15372ee8
--- /dev/null
+++ b/testing/src/main/kotlin/testing/IntToLongMapper.kt
@@ -0,0 +1,9 @@
+package testing
+
+import tech.mappie.api.ObjectMappie
+
+data class LongInput(val value: Long)
+
+data class IntOutput(val value: Int)
+
+object IntToLongMapper : ObjectMappie<LongInput, IntOutput>()
\ No newline at end of file
diff --git a/testing/src/main/kotlin/testing/ListToNullableListMapper.kt b/testing/src/main/kotlin/testing/ListToNullableListMapper.kt
index ddfd9d78..6b814266 100644
--- a/testing/src/main/kotlin/testing/ListToNullableListMapper.kt
+++ b/testing/src/main/kotlin/testing/ListToNullableListMapper.kt
@@ -14,4 +14,4 @@ object NullableListFromListMapper : ObjectMappie<SourceList, TargetList>() {
 
 object StringIdentityMapper : ObjectMappie<String, String>() {
     override fun map(from: String): String = from
-}
\ No newline at end of file
+}
diff --git a/testing/src/test/kotlin/testing/IdentityMapperTest.kt b/testing/src/test/kotlin/testing/IntIdentityMapperTest.kt
similarity index 65%
rename from testing/src/test/kotlin/testing/IdentityMapperTest.kt
rename to testing/src/test/kotlin/testing/IntIdentityMapperTest.kt
index e3c29fd7..8422337a 100644
--- a/testing/src/test/kotlin/testing/IdentityMapperTest.kt
+++ b/testing/src/test/kotlin/testing/IntIdentityMapperTest.kt
@@ -3,10 +3,10 @@ package testing
 import org.junit.jupiter.api.Test
 import kotlin.test.assertEquals
 
-class IdentityMapperTest {
+class IntIdentityMapperTest {
 
     @Test
     fun `map Int to Int via IdentityMapper`() {
-        assertEquals(1, IdentityMapper.map(1))
+        assertEquals(1, IntIdentityMapper.map(1))
     }
 }
\ No newline at end of file
diff --git a/testing/src/test/kotlin/testing/IntToLongMapperTest.kt b/testing/src/test/kotlin/testing/IntToLongMapperTest.kt
new file mode 100644
index 00000000..56a02b9a
--- /dev/null
+++ b/testing/src/test/kotlin/testing/IntToLongMapperTest.kt
@@ -0,0 +1,15 @@
+package testing
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class IntToLongMapperTest {
+
+    @Test
+    fun `map Int to Long via IntToLongMapper`() {
+        assertEquals(
+            IntOutput(1),
+            IntToLongMapper.map(LongInput(1)),
+        )
+    }
+}
\ No newline at end of file