diff --git a/modules/simple-java-mail/src/main/java/org/simplejavamail/converter/internal/mimemessage/MimeMessageParser.java b/modules/simple-java-mail/src/main/java/org/simplejavamail/converter/internal/mimemessage/MimeMessageParser.java
index d648dc047..d196c724c 100644
--- a/modules/simple-java-mail/src/main/java/org/simplejavamail/converter/internal/mimemessage/MimeMessageParser.java
+++ b/modules/simple-java-mail/src/main/java/org/simplejavamail/converter/internal/mimemessage/MimeMessageParser.java
@@ -208,7 +208,7 @@ public static String parseFileName(@NotNull final Part currentPart) {
 	 */
 	@SuppressWarnings("WeakerAccess")
 	public static String parseCalendarMethod(@NotNull MimePart currentPart) {
-		Pattern compile = Pattern.compile("method=\"(.*?)\"");
+		Pattern compile = Pattern.compile("method=\"?(\\w+)");
 		final String contentType;
 		try {
 			contentType = currentPart.getDataHandler().getContentType();