diff --git a/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/interpretation_utils.kt b/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/interpretation_utils.kt
index 778f7e8b5..d9578b0e9 100644
--- a/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/interpretation_utils.kt
+++ b/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/interpretation_utils.kt
@@ -54,7 +54,7 @@ fun CompilationUnit.activationGroupType(): ActivationGroupType? {
     }
 }
 
-fun ActivationGroupType.assignedName(current: RpgProgram, caller: RpgProgram?): String {
+fun ActivationGroupType.assignedName(caller: RpgProgram?): String {
     return when (this) {
         is CallerActivationGroup -> {
             require(caller != null) { "caller is mandatory" }
@@ -62,7 +62,6 @@ fun ActivationGroupType.assignedName(current: RpgProgram, caller: RpgProgram?):
         }
         is NewActivationGroup -> UUID.randomUUID().toString()
         is NamedActivationGroup -> groupName
-        else -> error("$this ActivationGroupType is not yet handled")
     }
 }
 
diff --git a/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/program.kt b/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/program.kt
index c885eceec..65e48b7c5 100644
--- a/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/program.kt
+++ b/rpgJavaInterpreter-core/src/main/kotlin/com/smeup/rpgparser/interpreter/program.kt
@@ -130,17 +130,21 @@ class RpgProgram(val cu: CompilationUnit, val name: String = "<UNNAMED RPG PROGR
                 } else {
                     null
                 }
-                val activationGroupType = cu.activationGroupType() ?: when (caller) {
 
-                        // for main program, which does not have a caller, activation group is fixed by config
-                        null -> NamedActivationGroup(MainExecutionContext.getConfiguration().defaultActivationGroupName)
-                        else -> {
-                            CallerActivationGroup
-                        }
+                val activationGroupType = cu.activationGroupType()?.let {
+                    when {
+                        // When there is no caller use the default activation group
+                        it is CallerActivationGroup && caller == null ->
+                            NamedActivationGroup(MainExecutionContext.getConfiguration().defaultActivationGroupName)
+                        else -> it
                     }
-                activationGroupType.let {
-                    activationGroup = ActivationGroup(it, it.assignedName(this, caller))
+                } ?: when (caller) {
+                    // for main program, which does not have a caller, activation group is fixed by config
+                    null -> NamedActivationGroup(MainExecutionContext.getConfiguration().defaultActivationGroupName)
+                    else -> CallerActivationGroup
                 }
+
+                activationGroup = ActivationGroup(activationGroupType, activationGroupType.assignedName(caller))
             }
             MainExecutionContext.getProgramStack().push(this)
             MainExecutionContext.getConfiguration().jarikoCallback.onEnterPgm(name, interpreter.getGlobalSymbolTable())
diff --git a/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/interpreter/ActivationGroupTest.kt b/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/interpreter/ActivationGroupTest.kt
index 000c36073..ab809d2fc 100644
--- a/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/interpreter/ActivationGroupTest.kt
+++ b/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/interpreter/ActivationGroupTest.kt
@@ -36,6 +36,30 @@ open class ActivationGroupTest : AbstractTest() {
         commandLineProgram.singleCall(emptyList(), conf)
     }
 
+    /**
+     * Assigned activation group name should be the default from configuration
+     * */
+    @Test
+    fun testUnspecifiedCaller() {
+        val pgm = "     H ACTGRP(*CALLER)\n" +
+                "     C                   SETON                                          RT"
+
+        val conf = Configuration(
+            jarikoCallback = JarikoCallback(
+                getActivationGroup = {
+                        _: String, associatedActivationGroup: ActivationGroup? ->
+                    println("associatedActivationGroupName: ${associatedActivationGroup?.assignedName}")
+                    assertEquals(Configuration().defaultActivationGroupName, associatedActivationGroup?.assignedName)
+                    assertEquals(DEFAULT_ACTIVATION_GROUP_NAME, associatedActivationGroup?.assignedName)
+                    null
+                }
+            )
+        )
+        conf.adaptForTestCase(this)
+        val commandLineProgram = getProgram(pgm)
+        commandLineProgram.singleCall(emptyList(), conf)
+    }
+
     /**
      * Assigned activation group name should be from declaration
      * */
diff --git a/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/smeup/MULANGT02ConstAndDSpecTest.kt b/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/smeup/MULANGT02ConstAndDSpecTest.kt
index 678a6b17b..e273da003 100644
--- a/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/smeup/MULANGT02ConstAndDSpecTest.kt
+++ b/rpgJavaInterpreter-core/src/test/kotlin/com/smeup/rpgparser/smeup/MULANGT02ConstAndDSpecTest.kt
@@ -352,4 +352,14 @@ open class MULANGT02ConstAndDSpecTest : MULANGTTest() {
         val expected = listOf("ok")
         assertEquals(expected, "smeup/MUDRNRAPU00219".outputOf(configuration = smeupConfig))
     }
+
+    /**
+     * Caller activation group with no actual caller
+     * @see #LS24003137
+     */
+    @Test
+    fun executeMUDRNRAPU00221() {
+        val expected = listOf("ok")
+        assertEquals(expected, "smeup/MUDRNRAPU00221".outputOf(configuration = smeupConfig))
+    }
 }
\ No newline at end of file
diff --git a/rpgJavaInterpreter-core/src/test/resources/smeup/MUDRNRAPU00221.rpgle b/rpgJavaInterpreter-core/src/test/resources/smeup/MUDRNRAPU00221.rpgle
new file mode 100644
index 000000000..04b255e26
--- /dev/null
+++ b/rpgJavaInterpreter-core/src/test/resources/smeup/MUDRNRAPU00221.rpgle
@@ -0,0 +1,5 @@
+     D £DBG_Str        S             2
+     H DECEDIT(*JOBRUN) DATEDIT(*DMY/) DFTACTGRP(*NO) ACTGRP(*CALLER)
+     H OPTION(*NODEBUGIO:*SRCSTMT:*NOUNREF) CCSID(*CHAR : *JOBRUN) DEBUG(*INPUT)
+     C                   EVAL      £DBG_Str='ok'
+     C     £DBG_Str      DSPLY
\ No newline at end of file