diff --git a/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt b/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt
index 69f9013678..c05ee4b314 100644
--- a/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt
+++ b/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt
@@ -17,11 +17,13 @@ import net.corda.core.serialization.SerializationContext
 import net.corda.core.serialization.SerializationFactory
 import net.corda.core.utilities.contextLogger
 import java.io.NotSerializableException
+import java.lang.Exception
 import java.security.PublicKey
 import java.time.Duration
 import java.time.Instant
 import java.util.ArrayDeque
 import java.util.UUID
+import java.util.regex.Pattern
 import kotlin.collections.ArrayList
 import kotlin.collections.component1
 import kotlin.collections.component2
@@ -67,6 +69,10 @@ open class TransactionBuilder(
         private fun defaultLockId() = (Strand.currentStrand() as? FlowStateMachine<*>)?.id?.uuid ?: UUID.randomUUID()
         private val log = contextLogger()
         private const val CORDA_VERSION_THAT_INTRODUCED_FLATTENED_COMMANDS = 4
+
+        private val ID_PATTERN = "\\p{javaJavaIdentifierStart}\\p{javaJavaIdentifierPart}*"
+        private val FQCP = Pattern.compile("$ID_PATTERN(/$ID_PATTERN)+")
+        private fun isValidJavaClass(identifier: String) = FQCP.matcher(identifier).matches()
     }
 
     private val inputsWithTransactionState = arrayListOf<StateAndRef<ContractState>>()
@@ -168,42 +174,52 @@ open class TransactionBuilder(
      * @return true if a new dependency was successfully added.
      */
     private fun addMissingDependency(services: ServicesForResolution, wireTx: WireTransaction): Boolean {
-        try {
+        return try {
             wireTx.toLedgerTransaction(services).verify()
-        } catch (e: NoClassDefFoundError) {
-            val missingClass = e.message ?: throw e
-            addMissingAttachment(missingClass, services)
-            return true
-        } catch (e: TransactionDeserialisationException) {
-            if (e.cause is NotSerializableException && e.cause.cause is ClassNotFoundException) {
-                val missingClass = e.cause.cause!!.message ?: throw e
-                addMissingAttachment(missingClass.replace(".", "/"), services)
-                return true
+            // The transaction verified successfully without adding any extra dependency.
+            false
+        } catch (e: Throwable) {
+            val rootError = e.rootCause
+            when {
+                // Handle various exceptions that can be thrown during verification and drill down the wrappings.
+                // Note: this is a best effort to preserve backwards compatibility.
+                rootError is ClassNotFoundException -> addMissingAttachment((rootError.message ?: throw e).replace(".", "/"), services, e)
+                rootError is NoClassDefFoundError -> addMissingAttachment(rootError.message ?: throw e, services, e)
+
+                // Ignore these exceptions as they will break unit tests.
+                // The point here is only to detect missing dependencies. The other exceptions are irrelevant.
+                e is TransactionVerificationException -> false
+                e is TransactionResolutionException -> false
+                e is IllegalStateException -> false
+                e is IllegalArgumentException -> false
+
+                // Fail early if none of the expected scenarios were hit.
+                else -> {
+                    log.error("""The transaction currently built will not validate because of an unknown error most likely caused by a
+                        missing dependency in the transaction attachments.
+                        Please contact the developer of the CorDapp for further instructions.
+                    """.trimIndent(), e)
+                    throw e
+                }
             }
-            return false
-        } catch (e: NotSerializableException) {
-            if (e.cause is ClassNotFoundException) {
-                val missingClass = e.cause!!.message ?: throw e
-                addMissingAttachment(missingClass.replace(".", "/"), services)
-                return true
-            }
-            return false
-        // Ignore these exceptions as they will break unit tests.
-        // The point here is only to detect missing dependencies. The other exceptions are irrelevant.
-        } catch (tve: TransactionVerificationException) {
-        } catch (tre: TransactionResolutionException) {
-        } catch (ise: IllegalStateException) {
-        } catch (ise: IllegalArgumentException) {
         }
-        return false
     }
 
-    private fun addMissingAttachment(missingClass: String, services: ServicesForResolution) {
+    private fun addMissingAttachment(missingClass: String, services: ServicesForResolution, originalException: Throwable): Boolean {
+        if (!isValidJavaClass(missingClass)) {
+            log.warn("Could not autodetect a valid attachment for the transaction being built.")
+            throw originalException
+        }
+
         val attachment = services.attachments.internalFindTrustedAttachmentForClass(missingClass)
-                ?: throw IllegalArgumentException("""The transaction currently built is missing an attachment for class: $missingClass.
+
+        if (attachment == null) {
+            log.error("""The transaction currently built is missing an attachment for class: $missingClass.
                         Attempted to find a suitable attachment but could not find any in the storage.
                         Please contact the developer of the CorDapp for further instructions.
                     """.trimIndent())
+            throw originalException
+        }
 
         log.warnOnce("""The transaction currently built is missing an attachment for class: $missingClass.
                         Automatically attaching contract dependency $attachment.
@@ -211,6 +227,7 @@ open class TransactionBuilder(
                     """.trimIndent())
 
         addAttachment(attachment.id)
+        return true
     }
 
     /**
diff --git a/samples/simm-valuation-demo/contracts-states/src/main/kotlin/net/corda/vega/plugin/customserializers/UnusedFinanceSerializers.kt b/samples/simm-valuation-demo/contracts-states/src/main/kotlin/net/corda/vega/plugin/customserializers/UnusedFinanceSerializers.kt
new file mode 100644
index 0000000000..fb2bb2ce37
--- /dev/null
+++ b/samples/simm-valuation-demo/contracts-states/src/main/kotlin/net/corda/vega/plugin/customserializers/UnusedFinanceSerializers.kt
@@ -0,0 +1,27 @@
+package net.corda.vega.plugin.customserializers
+
+import net.corda.core.serialization.SerializationCustomSerializer
+import net.corda.finance.contracts.asset.Cash
+import net.corda.finance.schemas.CashSchema
+
+/**
+ * This just references a random class from the finance Cordapp for testing purposes.
+ */
+@Suppress("UNUSED")
+class UnusedFinanceSerializer : SerializationCustomSerializer<CashSchema, UnusedFinanceSerializer.Proxy> {
+    class Proxy
+    override fun toProxy(obj: CashSchema): Proxy =Proxy()
+    override fun fromProxy(proxy: Proxy): CashSchema = CashSchema
+}
+
+class Unused
+@Suppress("UNUSED")
+class UnusedFinanceSerializer1 : SerializationCustomSerializer<Unused, UnusedFinanceSerializer1.Proxy> {
+    init {
+        // Just instantiate some finance class.
+        Cash()
+    }
+    class Proxy
+    override fun toProxy(obj: Unused): Proxy =Proxy()
+    override fun fromProxy(proxy: Proxy): Unused = Unused()
+}