diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index a8a22e2f2..e18753fd5 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -23,6 +23,8 @@ EvalState::EvalState()
     initNixExprHelpers();
 
     addPrimOps();
+
+    cacheTerms = getEnv("NIX_TERM_CACHE", "1") == "1";
 }
 
 
@@ -730,6 +732,8 @@ Expr evalExpr(EvalState & state, Expr e)
 
     state.nrEvaluated++;
 
+    if (!state.cacheTerms) return evalExpr2(state, e);
+    
     /* Consult the memo table to quickly get the normal form of
        previously evaluated expressions. */
     Expr nf = state.normalForms.get(e);
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 5699d455c..db3bcadc6 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -38,6 +38,8 @@ struct EvalState
     unsigned int nrEvaluated;
     unsigned int nrCached;
 
+    bool cacheTerms;
+
     EvalState();
 
     void addPrimOps();