diff --git a/src/node_modules/renderImgOrSvg.js b/src/node_modules/renderImgOrSvg.js
index eb93980..246eedc 100644
--- a/src/node_modules/renderImgOrSvg.js
+++ b/src/node_modules/renderImgOrSvg.js
@@ -95,7 +95,7 @@ module.exports = (render) => async (ctx, encodedCode, _next) => {
       debug('rendered SVG in DOM');
     } catch (e) {
       debug('mermaid failed to render SVG: %o', e);
-      ctx.throw(400, 'invalid encoded code');
+      ctx.throw(400, e);
     }
     await render(ctx, page, size);
   } catch (e) {
diff --git a/src/static/mermaid.mjs b/src/static/mermaid.mjs
index 22db0ce..2d3add2 100644
--- a/src/static/mermaid.mjs
+++ b/src/static/mermaid.mjs
@@ -1,7 +1,7 @@
 import mermaid from '../../node_modules/mermaid/dist/mermaid.esm.min.mjs';
 
-function isSyntaxErrorFromMermaid(code) {
-  return code.includes('Syntax error in graph') && code.includes('error-icon');
+function isUnknownDiagramError(code) {
+  return code.includes('UnknownDiagramError');
 }
 
 function setBgColor(svgElement, bgColor) {
@@ -54,10 +54,10 @@ async function render(definition, config, bgColor, size) {
     }
   } catch (error) {
     console.error('Failed to render', error);
-    if (isSyntaxErrorFromMermaid(error.toString())) {
-      throw new Error('Syntax error in graph');
+    if (isUnknownDiagramError(error.toString())) {
+      throw new Error('Unknown diagram error');
     }
-    throw error;
+    throw error.message;
   }
 }