diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3a6cfc6f..cbdc20dd 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### `Fixed`
 
+* [#142](https://github.com/nf-core/viralrecon/issues/142) - Unknown method invocation `toBytes` on String type
+
 ### `Added`
 
 * Update pipeline template to nf-core/tools `1.12`
diff --git a/main.nf b/main.nf
index 0c7b58ec..e6ccf689 100644
--- a/main.nf
+++ b/main.nf
@@ -3454,7 +3454,8 @@ workflow.onComplete {
     def email_html = html_template.toString()
 
     // Render the sendmail template
-    def smail_fields = [ email: email_address, subject: subject, email_txt: email_txt, email_html: email_html, projectDir: "$projectDir", mqcFile: mqc_report, mqcMaxSize: params.max_multiqc_email_size.toBytes() ]
+    def max_multiqc_email_size = params.max_multiqc_email_size as nextflow.util.MemoryUnit
+    def smail_fields = [ email: email_address, subject: subject, email_txt: email_txt, email_html: email_html, projectDir: "$projectDir", mqcFile: mqc_report, mqcMaxSize: max_multiqc_email_size.toBytes() ]
     def sf = new File("$projectDir/assets/sendmail_template.txt")
     def sendmail_template = engine.createTemplate(sf).make(smail_fields)
     def sendmail_html = sendmail_template.toString()