diff --git a/gradle/libs.versions.toml b/gradle/libs.versions.toml
index 1cd1fbb7d..d66f975c0 100644
--- a/gradle/libs.versions.toml
+++ b/gradle/libs.versions.toml
@@ -4,7 +4,7 @@ gradle-api = "8.11.1"
 junit-jupiter = "5.11.4"
 kctfork = "0.13.0"
 kotest = "6.2.5"
-kotlin = "2.4.10"
+kotlin = "2.4.20"
 kotlinx-serialization = "1.11.0"
 lombok = "1.18.48"
 maven-plugin-annotations = "3.16.0"
diff --git a/scip-kotlinc/build.gradle.kts b/scip-kotlinc/build.gradle.kts
index aad935acf..f6a40ba6b 100644
--- a/scip-kotlinc/build.gradle.kts
+++ b/scip-kotlinc/build.gradle.kts
@@ -26,6 +26,20 @@ dependencies {
 
 tasks.named<Test>("test") {
     maxHeapSize = "2g"
+    dependsOn("testKotlin240")
+}
+
+// The plugin runs inside the indexed project's compiler, which can predate our build compiler.
+val kotlin240TestRuntime = configurations.create("kotlin240TestRuntime") {
+    extendsFrom(configurations.testRuntimeClasspath.get())
+    resolutionStrategy.force("org.jetbrains.kotlin:kotlin-compiler-embeddable:2.4.0")
+}
+
+tasks.register<Test>("testKotlin240") {
+    useJUnitPlatform()
+    testClassesDirs = sourceSets.test.get().output.classesDirs
+    classpath = sourceSets.test.get().output + sourceSets.main.get().output + kotlin240TestRuntime
+    maxHeapSize = "2g"
 }
 
 tasks.named<ShadowJar>("shadowJar") {
diff --git a/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/AnalyzerCheckers.kt b/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/AnalyzerCheckers.kt
index 1251f3a8f..366752b21 100644
--- a/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/AnalyzerCheckers.kt
+++ b/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/AnalyzerCheckers.kt
@@ -26,6 +26,7 @@ import org.jetbrains.kotlin.fir.resolve.getContainingClassSymbol
 import org.jetbrains.kotlin.fir.resolve.providers.symbolProvider
 import org.jetbrains.kotlin.fir.resolve.toClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirAnonymousObjectSymbol
+import org.jetbrains.kotlin.fir.symbols.impl.FirClassLikeSymbol
 import org.jetbrains.kotlin.fir.symbols.impl.FirPropertySymbol
 import org.jetbrains.kotlin.fir.types.FirTypeRef
 import org.jetbrains.kotlin.lexer.KtTokens
@@ -74,7 +75,8 @@ open class AnalyzerCheckers(session: FirSession) : FirAdditionalCheckersExtensio
         override val classLikeCheckers: Set<FirClassLikeChecker> = setOf(SemanticClassLikeChecker())
         override val constructorCheckers: Set<FirConstructorChecker> =
             setOf(SemanticConstructorChecker())
-        override val simpleFunctionCheckers: Set<FirSimpleFunctionChecker> =
+        // The specialized checker property was renamed in Kotlin 2.4.20.
+        override val functionCheckers: Set<FirFunctionChecker> =
             setOf(SemanticSimpleFunctionChecker())
         override val anonymousFunctionCheckers: Set<FirAnonymousFunctionChecker> =
             setOf(SemanticAnonymousFunctionChecker())
@@ -278,9 +280,10 @@ open class AnalyzerCheckers(session: FirSession) : FirAdditionalCheckersExtensio
         }
     }
 
-    private class SemanticSimpleFunctionChecker : FirSimpleFunctionChecker(MppCheckerKind.Common) {
+    private class SemanticSimpleFunctionChecker : FirFunctionChecker(MppCheckerKind.Common) {
         context(context: CheckerContext, reporter: DiagnosticReporter)
-        override fun check(declaration: FirNamedFunction) {
+        override fun check(declaration: FirFunction) {
+            if (declaration !is FirNamedFunction) return
             val source = declaration.source ?: return
             val ktFile = context.containingFileSymbol?.sourceFile ?: return
             val visitor = visitors[ktFile]
@@ -388,9 +391,19 @@ open class AnalyzerCheckers(session: FirSession) : FirAdditionalCheckersExtensio
 
     private class SemanticResolvedQualifierChecker :
         FirResolvedQualifierChecker(MppCheckerKind.Common) {
+        companion object {
+            // Resolve once against the host compiler: symbol became qualifierSymbol in 2.4.20.
+            private val symbolGetter =
+                try {
+                    FirResolvedQualifier::class.java.getMethod("getQualifierSymbol")
+                } catch (_: NoSuchMethodException) {
+                    FirResolvedQualifier::class.java.getMethod("getSymbol")
+                }
+        }
+
         context(context: CheckerContext, reporter: DiagnosticReporter)
         override fun check(expression: FirResolvedQualifier) {
-            val symbol = expression.symbol ?: return
+            val symbol = symbolGetter.invoke(expression) as FirClassLikeSymbol<*>? ?: return
             val source = expression.source ?: return
             if (source.kind is KtFakeSourceElementKind) return
             val ktFile = context.containingFileSymbol?.sourceFile ?: return
diff --git a/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/PostAnalysisExtension.kt b/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/PostAnalysisExtension.kt
index e814439c5..211ca221e 100644
--- a/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/PostAnalysisExtension.kt
+++ b/scip-kotlinc/src/main/kotlin/org/scip_code/scip_java/kotlinc/PostAnalysisExtension.kt
@@ -12,6 +12,7 @@ import org.jetbrains.kotlin.cli.common.messages.MessageRenderer
 import org.jetbrains.kotlin.cli.common.messages.PrintingMessageCollector
 import org.jetbrains.kotlin.config.CommonConfigurationKeys
 import org.jetbrains.kotlin.config.CompilerConfiguration
+import org.jetbrains.kotlin.config.MessageCollectorAccess
 import org.jetbrains.kotlin.ir.declarations.IrModuleFragment
 import org.scip_code.scip.Document
 import org.scip_code.scip_java.shared.ScipShardPaths
@@ -61,6 +62,7 @@ class PostAnalysisExtension(
         return null
     }
 
+    @OptIn(MessageCollectorAccess::class)
     private val messageCollector =
         configuration.get(
             CommonConfigurationKeys.MESSAGE_COLLECTOR_KEY,