diff --git a/graphql-dgs-codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/CodeGen.kt b/graphql-dgs-codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/CodeGen.kt
index 193c89b8..96cc8573 100644
--- a/graphql-dgs-codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/CodeGen.kt
+++ b/graphql-dgs-codegen-core/src/main/kotlin/com/netflix/graphql/dgs/codegen/CodeGen.kt
@@ -145,6 +145,7 @@ class CodeGen private constructor(
             )
     }
 
+    private val dependencyTypeMappings = mutableMapOf<String, String>()
     private val document = buildDocument()
     private val schemaIndex = SchemaIndex(document)
     private val requiredTypes: Set<String> by lazy {
@@ -164,6 +165,13 @@ class CodeGen private constructor(
             typeName in requiredTypes
 
     fun generate(): CodeGenResult {
+        // Apply dependency mappings at generation time so callers can change their mappings after
+        // constructing CodeGen. User-provided mappings take precedence over dependency mappings.
+        // Without dependency mappings the caller's map is left untouched, as in 8.7.0.
+        if (dependencyTypeMappings.isNotEmpty()) {
+            config.typeMapping = dependencyTypeMappings + config.typeMapping
+        }
+
         val generated =
             when (config.language) {
                 Language.JAVA -> generateJava()
@@ -267,10 +275,10 @@ class CodeGen private constructor(
                         val props = Properties()
                         props.load(typeMappingInput)
 
-                        // Add the new type mappings from dependencies to existing type mappings.
-                        // The user provided config overrides mappings from the dependencies.
-                        @Suppress("UNCHECKED_CAST")
-                        config.typeMapping = (props as Map<String, String>).plus(config.typeMapping)
+                        // Earlier dependencies take precedence over later ones, matching the
+                        // previous merge order. User mappings are applied in generate().
+                        val mappings = props.stringPropertyNames().associateWith(props::getProperty)
+                        dependencyTypeMappings.putAll(mappings + dependencyTypeMappings)
                     }
                 }
 
diff --git a/graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/CodeGenTest.kt b/graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/CodeGenTest.kt
index ce2f24dd..a001390c 100644
--- a/graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/CodeGenTest.kt
+++ b/graphql-dgs-codegen-core/src/test/kotlin/com/netflix/graphql/dgs/codegen/CodeGenTest.kt
@@ -6883,6 +6883,143 @@ It takes a title and such.
         ).isEqualTo("java.lang.String")
     }
 
+    @Test
+    fun `Codegen should apply dependency type mappings after caller changes config`() {
+        val typeMappingDependency =
+            createSchemaJar(
+                """
+                type Query { invoice: Invoice }
+                type Invoice { money: Money }
+                type Money { amount: Int }
+                """.trimIndent(),
+                "Money=com.acme.Money",
+            )
+        val config =
+            CodeGenConfig(
+                schemaJarFilesFromDependencies = listOf(typeMappingDependency),
+                packageName = BASE_PACKAGE_NAME,
+            )
+        val codeGen = CodeGen(config)
+
+        assertThat(config.typeMapping).isEmpty()
+
+        config.typeMapping = mapOf("Other" to "x.Other")
+
+        val result = codeGen.generate()
+
+        assertThat(config.typeMapping)
+            .containsEntry("Money", "com.acme.Money")
+            .containsEntry("Other", "x.Other")
+        assertThat(result.javaDataTypes).noneMatch { it.typeSpec().name() == "Money" }
+        assertThat(
+            result.javaDataTypes
+                .single { it.typeSpec().name() == "Invoice" }
+                .typeSpec()
+                .fieldSpecs()
+                .single()
+                .type()
+                .toString(),
+        ).isEqualTo("com.acme.Money")
+
+        val repeatedResult = codeGen.generate()
+
+        assertThat(config.typeMapping)
+            .containsEntry("Money", "com.acme.Money")
+            .containsEntry("Other", "x.Other")
+        assertThat(repeatedResult.javaDataTypes.map { it.typeSpec().toString() })
+            .isEqualTo(result.javaDataTypes.map { it.typeSpec().toString() })
+
+        config.typeMapping = mapOf("Money" to "x.Money", "Other" to "x.Other")
+
+        assertThat(invoiceMoneyType(codeGen.generate())).isEqualTo("x.Money")
+        assertThat(config.typeMapping).containsEntry("Money", "x.Money")
+    }
+
+    @Test
+    fun `Codegen should honor caller map mutations between generate calls without dependency mappings`() {
+        val schema =
+            """
+            type Query { invoice: Invoice }
+            type Invoice { money: Money }
+            type Money { amount: Int }
+            """.trimIndent()
+        val callerMap = mutableMapOf<String, String>()
+        val config = CodeGenConfig(schemas = setOf(schema), packageName = BASE_PACKAGE_NAME, typeMapping = callerMap)
+        val codeGen = CodeGen(config)
+
+        assertThat(invoiceMoneyType(codeGen.generate())).isEqualTo("$BASE_PACKAGE_NAME.types.Money")
+
+        callerMap["Money"] = "com.acme.Money"
+
+        assertThat(invoiceMoneyType(codeGen.generate())).isEqualTo("com.acme.Money")
+        assertThat(config.typeMapping).isSameAs(callerMap)
+    }
+
+    @Test
+    fun `Codegen should honor caller map mutations when dependency jar has no type mappings`() {
+        val schemaJar =
+            createSchemaJar(
+                """
+                type Query { invoice: Invoice }
+                type Invoice { money: Money }
+                type Money { amount: Int }
+                """.trimIndent(),
+            )
+        val callerMap = mutableMapOf<String, String>()
+        val config =
+            CodeGenConfig(
+                schemaJarFilesFromDependencies = listOf(schemaJar),
+                packageName = BASE_PACKAGE_NAME,
+                typeMapping = callerMap,
+            )
+        val codeGen = CodeGen(config)
+
+        assertThat(invoiceMoneyType(codeGen.generate())).isEqualTo("$BASE_PACKAGE_NAME.types.Money")
+
+        callerMap["Money"] = "com.acme.Money"
+
+        assertThat(invoiceMoneyType(codeGen.generate())).isEqualTo("com.acme.Money")
+        assertThat(config.typeMapping).isSameAs(callerMap)
+    }
+
+    private fun invoiceMoneyType(result: CodeGenResult): String =
+        result.javaDataTypes
+            .single { it.typeSpec().name() == "Invoice" }
+            .typeSpec()
+            .fieldSpecs()
+            .single()
+            .type()
+            .toString()
+
+    @Test
+    fun `Codegen should preserve earlier dependency type mapping precedence`() {
+        val firstDependency =
+            createSchemaJar(
+                """
+                type Query { item: Item }
+                type Item { amount: Int }
+                """.trimIndent(),
+                "Item=com.acme.FirstItem",
+            )
+        val secondDependency =
+            createSchemaJar(
+                """
+                extend type Query { other: Other }
+                type Other { amount: Int }
+                """.trimIndent(),
+                "Item=com.acme.SecondItem",
+            )
+        val config =
+            CodeGenConfig(
+                schemaJarFilesFromDependencies = listOf(firstDependency, secondDependency),
+                packageName = BASE_PACKAGE_NAME,
+            )
+
+        CodeGen(config).generate()
+
+        assertThat(config.typeMapping).containsEntry("Item", "com.acme.FirstItem")
+    }
+
     @Test
     fun `Codegen should generate schema with unsigned int`() {
         val schema =