diff --git a/client/src/utils/format.js b/client/src/utils/format.js
index 616af68386..3cf2049750 100644
--- a/client/src/utils/format.js
+++ b/client/src/utils/format.js
@@ -3,5 +3,13 @@ import { inspect } from 'util';
 export function format(x) {
   // we're trying to mimic console.log, so we avoid wrapping strings in quotes:
   if (typeof x === 'string') return x;
+  else if (x instanceof Set) {
+    return `Set(${x.size}) {${Array.from(x).join(', ')}}`;
+  } else if (x instanceof Map) {
+    return `Map(${x.size}) {${Array.from(
+      x.entries(),
+      ([k, v]) => `${k} => ${v}`
+    ).join(', ')}})`;
+  }
   return inspect(x);
 }