diff --git a/components/nexusoperations/workflow/commands.go b/components/nexusoperations/workflow/commands.go
index 07e00d0baa7..8bb59fea126 100644
--- a/components/nexusoperations/workflow/commands.go
+++ b/components/nexusoperations/workflow/commands.go
@@ -109,9 +109,12 @@ func (ch *commandHandler) HandleScheduleCommand(
 	}
 
 	headerLength := 0
+	lowerCaseHeader := make(map[string]string, len(attrs.NexusHeader))
 	for k, v := range attrs.NexusHeader {
-		headerLength += len(k) + len(v)
-		if slices.Contains(ch.config.DisallowedOperationHeaders(), strings.ToLower(k)) {
+		lowerK := strings.ToLower(k)
+		lowerCaseHeader[lowerK] = v
+		headerLength += len(lowerK) + len(v)
+		if slices.Contains(ch.config.DisallowedOperationHeaders(), lowerK) {
 			return workflow.FailWorkflowTaskError{
 				Cause:   enumspb.WORKFLOW_TASK_FAILED_CAUSE_BAD_SCHEDULE_NEXUS_OPERATION_ATTRIBUTES,
 				Message: fmt.Sprintf("ScheduleNexusOperationCommandAttributes.NexusHeader contains a disallowed header key: %q", k),
@@ -158,7 +161,7 @@ func (ch *commandHandler) HandleScheduleCommand(
 				Operation:                    attrs.Operation,
 				Input:                        attrs.Input,
 				ScheduleToCloseTimeout:       attrs.ScheduleToCloseTimeout,
-				NexusHeader:                  attrs.NexusHeader,
+				NexusHeader:                  lowerCaseHeader,
 				RequestId:                    uuid.NewString(),
 				WorkflowTaskCompletedEventId: workflowTaskCompletedEventID,
 			},
diff --git a/service/frontend/workflow_handler.go b/service/frontend/workflow_handler.go
index 476ff6426b4..a6a96cd779b 100644
--- a/service/frontend/workflow_handler.go
+++ b/service/frontend/workflow_handler.go
@@ -5200,8 +5200,10 @@ func (wh *WorkflowHandler) validateWorkflowCompletionCallbacks(
 			}
 
 			headerSize := 0
+			lowerCaseHeaders := make(map[string]string, len(cb.Nexus.GetHeader()))
 			for k, v := range cb.Nexus.GetHeader() {
 				headerSize += len(k) + len(v)
+				lowerCaseHeaders[strings.ToLower(k)] = v
 			}
 			if headerSize > wh.config.CallbackHeaderMaxSize(ns.String()) {
 				return status.Error(
@@ -5212,6 +5214,7 @@ func (wh *WorkflowHandler) validateWorkflowCompletionCallbacks(
 					),
 				)
 			}
+			cb.Nexus.Header = lowerCaseHeaders
 		case *commonpb.Callback_Internal_:
 			// TODO(Tianyu): For now, there is nothing to validate given that this is an internal field.
 			continue