diff --git a/chrome/content/zotero/tools/csledit.xul b/chrome/content/zotero/tools/csledit.xul
index 5d3c72c864..920f5e09f3 100644
--- a/chrome/content/zotero/tools/csledit.xul
+++ b/chrome/content/zotero/tools/csledit.xul
@@ -101,7 +101,11 @@
 				}
 				var csl;
 				if (str.indexOf("<defaults") != -1) {
-					csl = new Zotero.CSL.Compat(str);
+					iframe.contentDocument.documentElement.innerHTML = 
+						'<div>'
+						+ "Old-style CSLs are no longer supported."
+						+ '</div>';
+					return;
 				}
 				else {
 					csl = new Zotero.CSL(str);
diff --git a/chrome/content/zotero/tools/cslpreview.xul b/chrome/content/zotero/tools/cslpreview.xul
index e4ce7b010b..711662519a 100644
--- a/chrome/content/zotero/tools/cslpreview.xul
+++ b/chrome/content/zotero/tools/cslpreview.xul
@@ -95,7 +95,7 @@
 				}
 				var csl;
 				if (str.indexOf("<defaults") != -1) {
-					csl = new Zotero.CSL.Compat(str);
+					return "Old-style CSLs are no longer supported.";
 				}
 				else {
 					csl = new Zotero.CSL(str);