diff --git a/mdl-examples/bug-tests/341-microflow-call-bson-field-order.mdl b/mdl-examples/bug-tests/341-microflow-call-bson-field-order.mdl
new file mode 100644
index 00000000..b4d75fac
--- /dev/null
+++ b/mdl-examples/bug-tests/341-microflow-call-bson-field-order.mdl
@@ -0,0 +1,61 @@
+-- ============================================================================
+-- Bug #341: Microflow call BSON field order produced CE0117 in Studio Pro
+-- ============================================================================
+--
+-- Symptom (before fix):
+--   `mxcli exec` could roundtrip the textual MDL of a microflow call
+--   (`$Result = call microflow Module.Target (Param = $Var);`) unchanged,
+--   but Studio Pro flagged the resulting activity with
+--     [CE0117] expression error on the call activity
+--   even though the MDL source had not been edited. The cause was BSON
+--   field order:
+--   - The writer emitted result-variable fields BEFORE the nested
+--     `MicroflowCall` document.
+--   - Inside `MicroflowCall`, `QueueSettings` was emitted BEFORE
+--     `ParameterMappings`.
+--   - Each `MicroflowCallParameterMapping` was emitted with `Parameter`
+--     BEFORE `Argument`.
+--   Studio Pro's expression validator depends on this order being stable
+--   to resolve parameter references.
+--
+-- After fix:
+--   `serializeMicroflowAction` now emits:
+--   - `MicroflowCallAction`: $ID, $Type, ErrorHandlingType, MicroflowCall,
+--     ResultVariableName, UseReturnVariable (call payload before result fields).
+--   - `MicroflowCall`: $ID, $Type, Microflow, ParameterMappings, QueueSettings.
+--   - `MicroflowCallParameterMapping`: $ID, $Type, Argument, Parameter.
+--
+-- Usage:
+--   mxcli exec mdl-examples/bug-tests/341-microflow-call-bson-field-order.mdl -p app.mpr
+--   mxcli -p app.mpr -c "describe microflow BugTest341.MF_Caller"
+--   `mx check` against the resulting MPR must report 0 errors and the
+--   call activity must not surface CE0117 in Studio Pro.
+-- ============================================================================
+
+create module BugTest341;
+
+create entity BugTest341.Item (
+  Name : string(100)
+);
+/
+
+-- Callee with one parameter, exercising the parameter-mapping serialization.
+create microflow BugTest341.MF_RenameItem (
+  $Item: BugTest341.Item,
+  $NewName: string
+)
+begin
+  change $Item (Name = $NewName);
+end;
+/
+
+-- Caller — produces a MicroflowCallAction whose nested MicroflowCall
+-- contains ParameterMappings. Field order in the serialized BSON must
+-- match Studio Pro's expectation.
+create microflow BugTest341.MF_Caller (
+  $Item: BugTest341.Item
+)
+begin
+  call microflow BugTest341.MF_RenameItem (Item = $Item, NewName = 'updated');
+end;
+/
diff --git a/sdk/mpr/microflow_call_writer_test.go b/sdk/mpr/microflow_call_writer_test.go
new file mode 100644
index 00000000..4df11fda
--- /dev/null
+++ b/sdk/mpr/microflow_call_writer_test.go
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: Apache-2.0
+
+package mpr
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/mendixlabs/mxcli/model"
+	"github.com/mendixlabs/mxcli/sdk/microflows"
+	"go.mongodb.org/mongo-driver/bson"
+)
+
+func TestMicroflowCallAction_WritesStableFieldOrder(t *testing.T) {
+	action := &microflows.MicroflowCallAction{
+		BaseElement:       model.BaseElement{ID: "action-id"},
+		ErrorHandlingType: microflows.ErrorHandlingTypeRollback,
+		MicroflowCall: &microflows.MicroflowCall{
+			BaseElement: model.BaseElement{ID: "call-id"},
+			Microflow:   "Demo.UpdateRecord",
+			ParameterMappings: []*microflows.MicroflowCallParameterMapping{
+				{
+					BaseElement: model.BaseElement{ID: "mapping-id"},
+					Argument:    "$Record/Name",
+					Parameter:   "Demo.UpdateRecord.Name",
+				},
+			},
+		},
+		UseReturnVariable: true,
+	}
+
+	doc := serializeMicroflowAction(action)
+	assertBSONKeys(t, doc, []string{
+		"$ID",
+		"$Type",
+		"ErrorHandlingType",
+		"MicroflowCall",
+		"ResultVariableName",
+		"UseReturnVariable",
+	})
+
+	callDoc, ok := bsonValue(doc, "MicroflowCall").(bson.D)
+	if !ok {
+		t.Fatalf("MicroflowCall type = %T, want bson.D", bsonValue(doc, "MicroflowCall"))
+	}
+	assertBSONKeys(t, callDoc, []string{
+		"$ID",
+		"$Type",
+		"Microflow",
+		"ParameterMappings",
+		"QueueSettings",
+	})
+
+	mappings, ok := bsonValue(callDoc, "ParameterMappings").(bson.A)
+	if !ok || len(mappings) != 2 {
+		t.Fatalf("ParameterMappings = %#v, want marker plus one mapping", bsonValue(callDoc, "ParameterMappings"))
+	}
+	mappingDoc, ok := mappings[1].(bson.D)
+	if !ok {
+		t.Fatalf("mapping type = %T, want bson.D", mappings[1])
+	}
+	assertBSONKeys(t, mappingDoc, []string{
+		"$ID",
+		"$Type",
+		"Argument",
+		"Parameter",
+	})
+}
+
+func assertBSONKeys(t *testing.T, doc bson.D, want []string) {
+	t.Helper()
+
+	var got []string
+	for _, elem := range doc {
+		got = append(got, elem.Key)
+	}
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("BSON keys = %#v, want %#v", got, want)
+	}
+}
+
+func bsonValue(doc bson.D, key string) any {
+	for _, elem := range doc {
+		if elem.Key == key {
+			return elem.Value
+		}
+	}
+	return nil
+}
diff --git a/sdk/mpr/writer_microflow_actions.go b/sdk/mpr/writer_microflow_actions.go
index 25c7ab08..304baed9 100644
--- a/sdk/mpr/writer_microflow_actions.go
+++ b/sdk/mpr/writer_microflow_actions.go
@@ -202,8 +202,6 @@ func serializeMicroflowAction(action microflows.MicroflowAction) bson.D {
 			{Key: "$ID", Value: idToBsonBinary(string(a.ID))},
 			{Key: "$Type", Value: "Microflows$MicroflowCallAction"},
 			{Key: "ErrorHandlingType", Value: stringOrDefault(string(a.ErrorHandlingType), "Rollback")},
-			{Key: "ResultVariableName", Value: a.ResultVariableName},
-			{Key: "UseReturnVariable", Value: a.UseReturnVariable},
 		}
 		// Serialize nested MicroflowCall structure
 		if a.MicroflowCall != nil {
@@ -211,7 +209,6 @@ func serializeMicroflowAction(action microflows.MicroflowAction) bson.D {
 				{Key: "$ID", Value: idToBsonBinary(string(a.MicroflowCall.ID))},
 				{Key: "$Type", Value: "Microflows$MicroflowCall"},
 				{Key: "Microflow", Value: a.MicroflowCall.Microflow},
-				{Key: "QueueSettings", Value: nil},
 			}
 			// Serialize parameter mappings within MicroflowCall
 			if len(a.MicroflowCall.ParameterMappings) > 0 {
@@ -221,8 +218,8 @@ func serializeMicroflowAction(action microflows.MicroflowAction) bson.D {
 					mapping := bson.D{
 						{Key: "$ID", Value: idToBsonBinary(string(pm.ID))},
 						{Key: "$Type", Value: "Microflows$MicroflowCallParameterMapping"},
-						{Key: "Parameter", Value: pm.Parameter},
 						{Key: "Argument", Value: pm.Argument},
+						{Key: "Parameter", Value: pm.Parameter},
 					}
 					mappings = append(mappings, mapping)
 				}
@@ -230,8 +227,13 @@ func serializeMicroflowAction(action microflows.MicroflowAction) bson.D {
 			} else {
 				mfCall = append(mfCall, bson.E{Key: "ParameterMappings", Value: bson.A{int32(2)}}) // Empty array with marker
 			}
+			mfCall = append(mfCall, bson.E{Key: "QueueSettings", Value: nil})
 			doc = append(doc, bson.E{Key: "MicroflowCall", Value: mfCall})
 		}
+		doc = append(doc,
+			bson.E{Key: "ResultVariableName", Value: a.ResultVariableName},
+			bson.E{Key: "UseReturnVariable", Value: a.UseReturnVariable},
+		)
 		return doc
 
 	case *microflows.JavaActionCallAction: