diff --git a/buildSrc/src/main/kotlin/BuildExtensions.kt b/buildSrc/src/main/kotlin/BuildExtensions.kt
index 5214f6e41..e92238c26 100644
--- a/buildSrc/src/main/kotlin/BuildExtensions.kt
+++ b/buildSrc/src/main/kotlin/BuildExtensions.kt
@@ -40,7 +40,9 @@ import io.spine.dependency.test.Kover
 import io.spine.gradle.repo.standardToSpineSdk
 import org.gradle.api.Project
 import org.gradle.api.Task
+import org.gradle.api.file.DuplicatesStrategy
 import org.gradle.api.tasks.JavaExec
+import org.gradle.jvm.tasks.Jar
 import org.gradle.kotlin.dsl.ScriptHandlerScope
 import org.gradle.plugin.use.PluginDependenciesSpec
 import org.gradle.plugin.use.PluginDependencySpec
@@ -347,3 +349,15 @@ val buildToolConfigurations: Array<String> = arrayOf(
     "ksp",
     "dokka",
 )
+
+/**
+ * Make the `sourcesJar` task accept duplicated input which seems to occur
+ * somewhere inside Protobuf Gradle Plugin.
+ */
+fun Project.allowDuplicationInSourcesJar() {
+    tasks.withType(Jar::class.java).configureEach {
+        if (name == "sourcesJar") {
+            duplicatesStrategy = DuplicatesStrategy.INCLUDE
+        }
+    }
+}
diff --git a/gradle/wrapper/gradle-wrapper.jar b/gradle/wrapper/gradle-wrapper.jar
index 1b33c55ba..8bdaf60c7 100644
Binary files a/gradle/wrapper/gradle-wrapper.jar and b/gradle/wrapper/gradle-wrapper.jar differ
diff --git a/gradle/wrapper/gradle-wrapper.properties b/gradle/wrapper/gradle-wrapper.properties
index ff23a68d7..2e1113280 100644
--- a/gradle/wrapper/gradle-wrapper.properties
+++ b/gradle/wrapper/gradle-wrapper.properties
@@ -1,6 +1,6 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-8.14.2-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-9.1.0-bin.zip
 networkTimeout=10000
 validateDistributionUrl=true
 zipStoreBase=GRADLE_USER_HOME