Index: lams_central/web/groups.jsp
===================================================================
diff -u -redece7093e248662435cbb9a70536f8aff7cbb85 -r6ffc2de36c44bd95e1279aed102e7257b9f064f3
--- lams_central/web/groups.jsp	(.../groups.jsp)	(revision edece7093e248662435cbb9a70536f8aff7cbb85)
+++ lams_central/web/groups.jsp	(.../groups.jsp)	(revision 6ffc2de36c44bd95e1279aed102e7257b9f064f3)
@@ -238,7 +238,7 @@
 							<input type="hidden" name="lessonID" value='<c:out value="${lessonID}" />' />
 							<lams:FileUpload5 fileFieldname="groupUploadFile" fileInputMessageKey="label.upload.group.spreadsheet"
 											  uploadInfoMessageKey="-" maxFileSize="${UPLOAD_FILE_MAX_SIZE_AS_USER_STRING}"/>
-							<button id="import" type="button" class="btn btn-primary btn-disable-on-downupload ms-3"
+							<button id="import" type="button" class="btn btn-primary btn-disable-on-downupload ms-3 d-none"
 									onClick="javascript:importGroupsFromSpreadsheet()">
 								<i class="fa fa-upload"></i> <fmt:message key="button.import" />
 							</button>
Index: lams_central/web/includes/javascript/groups.js
===================================================================
diff -u -rfbc37c9e02e9215f623577fe2dd09d1701e78027 -r6ffc2de36c44bd95e1279aed102e7257b9f064f3
--- lams_central/web/includes/javascript/groups.js	(.../groups.js)	(revision fbc37c9e02e9215f623577fe2dd09d1701e78027)
+++ lams_central/web/includes/javascript/groups.js	(.../groups.js)	(revision 6ffc2de36c44bd95e1279aed102e7257b9f064f3)
@@ -39,6 +39,11 @@
 		// the label is "Group X" where X is the top group number
 		addGroup(null, LABELS.GROUP_PREFIX_LABEL + ' ' + $('#groupsCell .groupContainer').length, null);
 	});
+
+	$('#groupUploadFile').change(function(){
+		let fileName = $(this).val();
+		$('#import').toggleClass('d-none', !fileName || !fileName.endsWith('.xls'));
+	});
 });