diff --git a/nix-repl.cc b/nix-repl.cc
index ef9be417a..8049008d1 100644
--- a/nix-repl.cc
+++ b/nix-repl.cc
@@ -216,8 +216,10 @@ void NixRepl::completePrefix(string prefix)
 
         } catch (ParseError & e) {
             // Quietly ignore parse errors.
-        }catch (EvalError & e) {
+        } catch (EvalError & e) {
             // Quietly ignore evaluation errors.
+        } catch (UndefinedVarError & e) {
+            // Quietly ignore undefined variable errors.
         }
     }
 }