diff --git a/daffodil-core/src/main/scala/org/apache/daffodil/unparsers/runtime1/StringLengthUnparsers.scala b/daffodil-core/src/main/scala/org/apache/daffodil/unparsers/runtime1/StringLengthUnparsers.scala
index 49e1b31afc..0b2be365bc 100644
--- a/daffodil-core/src/main/scala/org/apache/daffodil/unparsers/runtime1/StringLengthUnparsers.scala
+++ b/daffodil-core/src/main/scala/org/apache/daffodil/unparsers/runtime1/StringLengthUnparsers.scala
@@ -26,6 +26,7 @@ import org.apache.daffodil.runtime1.processors.CharsetEv
 import org.apache.daffodil.runtime1.processors.ElementRuntimeData
 import org.apache.daffodil.runtime1.processors.Evaluatable
 import org.apache.daffodil.runtime1.processors.LengthEv
+import org.apache.daffodil.runtime1.processors.SuspendableOperation
 import org.apache.daffodil.runtime1.processors.TextTruncationType
 import org.apache.daffodil.runtime1.processors.UnparseTargetLengthInBitsEv
 import org.apache.daffodil.runtime1.processors.unparsers.*
@@ -70,10 +71,26 @@ class StringNoTruncateUnparser(erd: ElementRuntimeData)
 sealed abstract class StringSpecifiedLengthUnparserTruncateBase(
   stringTruncationType: TextTruncationType.Type,
   erd: ElementRuntimeData
-) extends StringSpecifiedLengthUnparserBase(erd) {
+) extends StringSpecifiedLengthUnparserBase(erd)
+  with SuspendableUnparser {
 
   Assert.usage(stringTruncationType ne TextTruncationType.None)
 
+  /**
+   * The target length the string is truncated to. It can depend on an
+   * outputValueCalc element that has not been computed yet.
+   */
+  protected[runtime1] def targetLengthEv: Evaluatable[AnyRef]
+
+  /**
+   * Reads the target length without retrying, so it must only be called
+   * once the target length can be evaluated.
+   */
+  protected[runtime1] def unparseString(state: UState): Unit
+
+  override protected def suspendableOperation =
+    new StringTruncationSuspendableOperation(erd, this)
+
   /**
    * We only truncate strings, and only if textStringJustification is left or
    * right, and only if truncateSpecifiedLengthString is yes.
@@ -122,6 +139,8 @@ class StringMaybeTruncateBitsUnparser(
 
   override val runtimeDependencies = Array(targetLengthInBitsEv, charsetEv)
 
+  override protected[runtime1] def targetLengthEv = targetLengthInBitsEv
+
   private def getLengthInBits(str: String, state: UState): (Long, Long) = {
     val cs = charsetEv.evaluate(state)
     val mfw = cs.maybeFixedWidth
@@ -171,7 +190,7 @@ class StringMaybeTruncateBitsUnparser(
     res
   }
 
-  override def unparse(state: UState): Unit = {
+  override protected[runtime1] def unparseString(state: UState): Unit = {
 
     //
     // We have to stage the bits of the value just so as to be able to count them
@@ -259,7 +278,9 @@ class StringMaybeTruncateCharactersUnparser(
 
   override val runtimeDependencies = Array(lengthInCharactersEv)
 
-  override def unparse(state: UState): Unit = {
+  override protected[runtime1] def targetLengthEv = lengthInCharactersEv
+
+  override protected[runtime1] def unparseString(state: UState): Unit = {
     val dos = state.getDataOutputStream
     val valueString = contentString(state)
     val targetLengthInCharacters =
@@ -285,3 +306,27 @@ class StringMaybeTruncateCharactersUnparser(
     Assert.invariant(nCharsWritten == valueToWrite.length)
   }
 }
+
+/**
+ * Suspends until the target length can be evaluated, then unparses the
+ * string, because the truncating string unparsers read the target length
+ * without retrying.
+ */
+class StringTruncationSuspendableOperation(
+  override val rd: ElementRuntimeData,
+  unparser: StringSpecifiedLengthUnparserTruncateBase
+) extends SuspendableOperation {
+
+  override def toString = "string truncation for " + rd.diagnosticDebugName
+
+  // Evaluating throws a RetryableException while the length is unavailable,
+  // which blocks this operation.
+  override protected def test(ustate: UState): Boolean = {
+    unparser.targetLengthEv.evaluate(ustate)
+    true
+  }
+
+  override protected def continuation(ustate: UState): Unit = {
+    unparser.unparseString(ustate)
+  }
+}
diff --git a/daffodil-test/src/test/resources/org/apache/daffodil/section00/general/testUnparserGeneral.tdml b/daffodil-test/src/test/resources/org/apache/daffodil/section00/general/testUnparserGeneral.tdml
index 549cef2799..4940801eb0 100644
--- a/daffodil-test/src/test/resources/org/apache/daffodil/section00/general/testUnparserGeneral.tdml
+++ b/daffodil-test/src/test/resources/org/apache/daffodil/section00/general/testUnparserGeneral.tdml
@@ -1023,8 +1023,7 @@
       </tdml:dfdlInfoset>
     </tdml:infoset>
     <tdml:errors>
-      <tdml:error>not have a value</tdml:error>
-      <tdml:error>circular dependency</tdml:error>
+      <tdml:error>circularly deadlocked</tdml:error>
     </tdml:errors>
   </tdml:unparserTestCase>
 
@@ -1055,10 +1054,7 @@
         </ex:e1>
       </tdml:dfdlInfoset>
     </tdml:infoset>
-    <tdml:errors>
-      <tdml:error>not have a value</tdml:error>
-      <tdml:error>circular dependency</tdml:error>
-    </tdml:errors>
+    <tdml:document>5ABCDE</tdml:document>
   </tdml:unparserTestCase>
 
     <tdml:defineSchema name="truncatedString3">
@@ -1113,7 +1109,7 @@
       </tdml:dfdlInfoset>
     </tdml:infoset>
     <tdml:errors>
-      <tdml:error>Value length unknown</tdml:error>
+      <tdml:error>circularly deadlocked</tdml:error>
     </tdml:errors>
   </tdml:unparserTestCase>