diff --git a/src/client/attachment.go b/src/client/attachment.go
index a51d902..5688506 100644
--- a/src/client/attachment.go
+++ b/src/client/attachment.go
@@ -44,6 +44,9 @@ func (attachmentEntry *AttachmentEntry) extractMetaData(attachmentData string) {
 	}
 
 	attachmentEntry.Base64 = attachmentData[base64FlagIndex+len("base64,"):]
+	if base64FlagIndex == 0 {
+		return
+	}
 	metaDataKeys := map[string]string{
 		"data:":     "MimeInfo",
 		"filename=": "FileName",
diff --git a/src/client/attachment_test.go b/src/client/attachment_test.go
index 8e4e711..1482ad2 100644
--- a/src/client/attachment_test.go
+++ b/src/client/attachment_test.go
@@ -45,6 +45,9 @@ func Test_Attachment_ExtractMetadata_ShouldPrepareDataFor_toDataForSignal(t *tes
 		{
 			"-base64 +data +filename", "data:someData;filename=file.name;INVALIDMTIzNDU=", false, "data:someData;filename=file.name;INVALIDMTIzNDU=", false, "", "", "data:someData;filename=file.name;INVALIDMTIzNDU=",
 		},
+		{
+			"base64 prefix at start +data", "base64,data:someData", false, "data:someData", false, "", "", "data:someData",
+		},
 	}
 
 	attachmentTmp := flag.String("attachment-tmp-dir", string(os.PathSeparator)+"tmp"+string(os.PathSeparator), "Attachment tmp directory")