diff --git a/core/src/main/kotlin/net/corda/core/internal/CordaUtils.kt b/core/src/main/kotlin/net/corda/core/internal/CordaUtils.kt
index 8c4be6530f..6595851d22 100644
--- a/core/src/main/kotlin/net/corda/core/internal/CordaUtils.kt
+++ b/core/src/main/kotlin/net/corda/core/internal/CordaUtils.kt
@@ -20,12 +20,15 @@ import org.slf4j.MDC
 const val PLATFORM_VERSION = 4
 
 fun ServicesForResolution.ensureMinimumPlatformVersion(requiredMinPlatformVersion: Int, feature: String) {
-    val currentMinPlatformVersion = networkParameters.minimumPlatformVersion
-    if (currentMinPlatformVersion < requiredMinPlatformVersion) {
+    checkMinimumPlatformVersion(networkParameters.minimumPlatformVersion, requiredMinPlatformVersion, feature)
+}
+
+fun checkMinimumPlatformVersion(minimumPlatformVersion: Int, requiredMinPlatformVersion: Int, feature: String) {
+    if (minimumPlatformVersion < requiredMinPlatformVersion) {
         throw ZoneVersionTooLowException(
                 "$feature requires all nodes on the Corda compatibility zone to be running at least platform version " +
                         "$requiredMinPlatformVersion. The current zone is only enforcing a minimum platform version of " +
-                        "$currentMinPlatformVersion. Please contact your zone operator."
+                        "$minimumPlatformVersion. Please contact your zone operator."
         )
     }
 }
diff --git a/core/src/main/kotlin/net/corda/core/transactions/LedgerTransaction.kt b/core/src/main/kotlin/net/corda/core/transactions/LedgerTransaction.kt
index adf63a000a..e584706be7 100644
--- a/core/src/main/kotlin/net/corda/core/transactions/LedgerTransaction.kt
+++ b/core/src/main/kotlin/net/corda/core/transactions/LedgerTransaction.kt
@@ -7,6 +7,7 @@ import net.corda.core.crypto.isFulfilledBy
 import net.corda.core.identity.Party
 import net.corda.core.internal.AttachmentWithContext
 import net.corda.core.internal.castIfPossible
+import net.corda.core.internal.checkMinimumPlatformVersion
 import net.corda.core.internal.uncheckedCast
 import net.corda.core.node.NetworkParameters
 import net.corda.core.serialization.CordaSerializable
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 a449440c09..0915f295c9 100644
--- a/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt
+++ b/core/src/main/kotlin/net/corda/core/transactions/TransactionBuilder.kt
@@ -95,6 +95,10 @@ open class TransactionBuilder @JvmOverloads constructor(
     private val inputsWithTransactionState = arrayListOf<TransactionState<ContractState>>()
     private val referencesWithTransactionState = arrayListOf<TransactionState<ContractState>>()
 
+    companion object {
+        private val log = contextLogger()
+    }
+
     /**
      * Creates a copy of the builder.
      */
diff --git a/core/src/test/kotlin/net/corda/core/transactions/TransactionBuilderTest.kt b/core/src/test/kotlin/net/corda/core/transactions/TransactionBuilderTest.kt
index cd9456cdc3..ecfdabdf20 100644
--- a/core/src/test/kotlin/net/corda/core/transactions/TransactionBuilderTest.kt
+++ b/core/src/test/kotlin/net/corda/core/transactions/TransactionBuilderTest.kt
@@ -8,6 +8,7 @@ import net.corda.core.crypto.CompositeKey
 import net.corda.core.crypto.SecureHash
 import net.corda.core.identity.Party
 import net.corda.core.internal.AbstractAttachment
+import net.corda.core.internal.PLATFORM_VERSION
 import net.corda.core.node.ServicesForResolution
 import net.corda.core.node.ZoneVersionTooLowException
 import net.corda.core.node.services.AttachmentStorage
@@ -40,7 +41,7 @@ class TransactionBuilderTest {
         val cordappProvider = rigorousMock<CordappProvider>()
         doReturn(cordappProvider).whenever(services).cordappProvider
         doReturn(contractAttachmentId).whenever(cordappProvider).getContractAttachmentID(DummyContract.PROGRAM_ID)
-        doReturn(testNetworkParameters()).whenever(services).networkParameters
+        doReturn(testNetworkParameters(minimumPlatformVersion = PLATFORM_VERSION)).whenever(services).networkParameters
 
         val attachmentStorage = rigorousMock<AttachmentStorage>()
         doReturn(attachmentStorage).whenever(services).attachments
diff --git a/docs/source/api-contract-constraints.rst b/docs/source/api-contract-constraints.rst
index 8d3a953086..d288ef5eb1 100644
--- a/docs/source/api-contract-constraints.rst
+++ b/docs/source/api-contract-constraints.rst
@@ -97,6 +97,10 @@ and the smoothest to deploy: no restarts or contract upgrade transactions are ne
 When CorDapp is build using :ref:`corda-gradle-plugin <cordapp_build_system_signing_cordapp_jar_ref>` the JAR is signed
 by Corda development key by default, an external keystore can be configured or signing can be disabled.
 
+.. warning:: CorDapps can only use signature constraints when participating in a Corda network using a minimum platform version of 4.
+    An auto downgrade rule applies to signed CorDapps built and tested with Corda 4 but running on a Corda network of a lower version:
+    if the associated contract class is whitelisted in the network parameters then zone constraints are applied, otherwise hash constraints are used.
+
 **Defaults.** Currently, the default constraint type is either a zone constraint, if the network parameters in effect when the
 transaction is built contain an entry for that contract class, or a hash constraint if not. Once the Signature Constraints are introduced,
 the default constraint will be the Signature Constraint if the jar is signed.