diff --git a/src/libcmd/command.hh b/src/libcmd/command.hh
index 354877bc5..454197b1c 100644
--- a/src/libcmd/command.hh
+++ b/src/libcmd/command.hh
@@ -276,6 +276,6 @@ void printClosureDiff(
 void runRepl(
     ref<EvalState> evalState,
     const Expr & expr,
-    const std::map<std::string, Value *> & extraEnv);
+    const ValMap & extraEnv);
 
 }
diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 37e454b21..950195572 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -1016,7 +1016,7 @@ std::ostream & NixRepl::printValue(std::ostream & str, Value & v, unsigned int m
 void runRepl(
     ref<EvalState> evalState,
     const Expr &expr,
-    const std::map<std::string, Value *> & extraEnv)
+    const ValMap & extraEnv)
 {
     auto repl = std::make_unique<NixRepl>(evalState);
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 22f034e27..65b1466ea 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -37,7 +37,11 @@ struct PrimOp
     const char * doc = nullptr;
 };
 
-typedef std::map<std::string, Value *> ValMap;
+#if HAVE_BOEHMGC
+    typedef std::map<std::string, Value *, std::less<std::string>, traceable_allocator<std::pair<const std::string, Value *> > > ValMap;
+#else
+    typedef std::map<std::string, Value *> ValMap;
+#endif
 
 struct Env
 {