diff --git a/src/libcmd/include/nix/cmd/repl.hh b/src/libcmd/include/nix/cmd/repl.hh
index 83e39727f..2cb46c69d 100644
--- a/src/libcmd/include/nix/cmd/repl.hh
+++ b/src/libcmd/include/nix/cmd/repl.hh
@@ -11,7 +11,7 @@ struct AbstractNixRepl
     Bindings * autoArgs;
 
     AbstractNixRepl(ref<EvalState> state)
-        : state(state)
+        : state(state), autoArgs(nullptr)
     { }
 
     virtual ~AbstractNixRepl()