diff --git a/core/src/main/kotlin/net/corda/core/crypto/SecureHash.kt b/core/src/main/kotlin/net/corda/core/crypto/SecureHash.kt
index c804fb63f8..c939f427b4 100644
--- a/core/src/main/kotlin/net/corda/core/crypto/SecureHash.kt
+++ b/core/src/main/kotlin/net/corda/core/crypto/SecureHash.kt
@@ -16,6 +16,7 @@ import net.corda.core.utilities.OpaqueBytes
 import net.corda.core.utilities.parseAsHex
 import net.corda.core.utilities.toHexString
 import java.security.MessageDigest
+import java.util.function.Supplier
 
 /**
  * Container for a cryptographically secure hash value.
@@ -64,16 +65,14 @@ sealed class SecureHash(bytes: ByteArray) : OpaqueBytes(bytes) {
             }
         }
 
-        private val threadLocalSha256MessageDigest = object : FastThreadLocal<MessageDigest>() {
-            override fun initialValue() = MessageDigest.getInstance("SHA-256")
-        }
+        private val sha256MessageDigest = SHA256DigestSupplier()
 
         /**
          * Computes the SHA-256 hash value of the [ByteArray].
          * @param bytes The [ByteArray] to hash.
          */
         @JvmStatic
-        fun sha256(bytes: ByteArray) = SHA256(threadLocalSha256MessageDigest.get().digest(bytes))
+        fun sha256(bytes: ByteArray) = SHA256(sha256MessageDigest.get().digest(bytes))
 
         /**
          * Computes the SHA-256 hash of the [ByteArray], and then computes the SHA-256 hash of the hash.
@@ -119,4 +118,17 @@ fun ByteArray.sha256(): SecureHash.SHA256 = SecureHash.sha256(this)
  */
 fun OpaqueBytes.sha256(): SecureHash.SHA256 = SecureHash.sha256(this.bytes)
 
+/**
+ * Hide the [FastThreadLocal] class behind a [Supplier] interface
+ * so that we can remove it for core-deterministic.
+ */
+private class SHA256DigestSupplier : Supplier<MessageDigest> {
+    private val threadLocalSha256MessageDigest = LocalSHA256Digest()
+    override fun get(): MessageDigest = threadLocalSha256MessageDigest.get()
+}
 
+// Declaring this as "object : FastThreadLocal<>" would have
+// created an extra public class in the API definition.
+private class LocalSHA256Digest : FastThreadLocal<MessageDigest>() {
+    override fun initialValue(): MessageDigest = MessageDigest.getInstance("SHA-256")
+}