diff --git a/node/src/test/kotlin/net/corda/node/internal/cordapp/CordappProviderImplTests.kt b/node/src/test/kotlin/net/corda/node/internal/cordapp/CordappProviderImplTests.kt
index f981b11e24..2bd8a10258 100644
--- a/node/src/test/kotlin/net/corda/node/internal/cordapp/CordappProviderImplTests.kt
+++ b/node/src/test/kotlin/net/corda/node/internal/cordapp/CordappProviderImplTests.kt
@@ -18,6 +18,7 @@ import java.io.FileOutputStream
 import java.lang.IllegalStateException
 import java.net.URL
 import java.nio.file.Files
+import java.util.Arrays.asList
 import java.util.jar.JarOutputStream
 import java.util.zip.Deflater.NO_COMPRESSION
 import java.util.zip.ZipEntry
@@ -200,8 +201,11 @@ class CordappProviderImplTests {
             val duplicateJarPath = signedJarPath.parent.resolve("duplicate-" + signedJarPath.fileName)
 
             Files.copy(signedJarPath, duplicateJarPath)
-            assertFailsWith<IllegalStateException> {
-                newCordappProvider(signedJarPath.toUri().toURL(), duplicateJarPath.toUri().toURL())
+            val urls = asList(signedJarPath.toUri().toURL(), duplicateJarPath.toUri().toURL())
+            JarScanningCordappLoader.fromJarUrls(urls, VersionInfo.UNKNOWN).use {
+                assertFailsWith<IllegalStateException> {
+                    CordappProviderImpl(it, stubConfigProvider, attachmentStore).apply { start() }
+                }
             }
         }
     }
@@ -212,8 +216,11 @@ class CordappProviderImplTests {
         SelfCleaningDir().use { file ->
             val jarA = ContractJarTestUtils.makeTestContractJar(file.path, listOf("com.example.MyContract", "com.example.AnotherContractForA"), generateManifest = false, jarFileName = "sampleA.jar")
             val jarB = ContractJarTestUtils.makeTestContractJar(file.path, listOf("com.example.MyContract", "com.example.AnotherContractForB"), generateManifest = false, jarFileName = "sampleB.jar")
-            assertFailsWith<IllegalStateException> {
-                newCordappProvider(jarA.toUri().toURL(), jarB.toUri().toURL())
+            val urls = asList(jarA.toUri().toURL(), jarB.toUri().toURL())
+            JarScanningCordappLoader.fromJarUrls(urls, VersionInfo.UNKNOWN).use {
+                assertFailsWith<IllegalStateException> {
+                    CordappProviderImpl(it, stubConfigProvider, attachmentStore).apply { start() }
+                }
             }
         }
     }
diff --git a/testing/test-utils/src/main/kotlin/net/corda/testing/core/internal/JarSignatureTestUtils.kt b/testing/test-utils/src/main/kotlin/net/corda/testing/core/internal/JarSignatureTestUtils.kt
index 00a827c1e1..4c21340f84 100644
--- a/testing/test-utils/src/main/kotlin/net/corda/testing/core/internal/JarSignatureTestUtils.kt
+++ b/testing/test-utils/src/main/kotlin/net/corda/testing/core/internal/JarSignatureTestUtils.kt
@@ -12,6 +12,7 @@ import java.nio.file.Files
 import java.nio.file.NoSuchFileException
 import java.nio.file.Path
 import java.nio.file.Paths
+import java.nio.file.StandardCopyOption.REPLACE_EXISTING
 import java.security.PublicKey
 import java.util.jar.Attributes
 import java.util.jar.JarInputStream
@@ -88,12 +89,13 @@ object JarSignatureTestUtils {
             JarInputStream(FileInputStream((this / fileName).toFile())).use(JarSignatureCollector::collectSigners)
 
     fun Path.addManifest(fileName: String, vararg entries: Pair<Attributes.Name, String>) {
+        val outputFile = this / (fileName + "Output")
         JarInputStream(FileInputStream((this / fileName).toFile())).use { input ->
             val manifest = input.manifest ?: Manifest()
             entries.forEach { (attributeName, value) ->
                 manifest.mainAttributes[attributeName] = value
             }
-            val output = JarOutputStream(FileOutputStream((this / fileName).toFile()), manifest)
+            val output = JarOutputStream(FileOutputStream(outputFile.toFile()), manifest)
             var entry = input.nextEntry
             val buffer = ByteArray(1 shl 14)
             while (true) {
@@ -108,5 +110,6 @@ object JarSignatureTestUtils {
             }
             output.close()
         }
+        Files.copy(outputFile, this / fileName, REPLACE_EXISTING)
     }
 }