diff --git a/nix-repl.cc b/nix-repl.cc
index 474ad4fc9..25f84a308 100644
--- a/nix-repl.cc
+++ b/nix-repl.cc
@@ -255,7 +255,7 @@ bool isVarName(const string & s)
         if (!((i >= 'a' && i <= 'z') ||
               (i >= 'A' && i <= 'Z') ||
               (i >= '0' && i <= '9') ||
-              i == '_' || i == '\''))
+              i == '_' || i == '-' || i == '\''))
             return false;
     return true;
 }