diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 3aa35b3276..c58b951268 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -148,8 +148,6 @@ EvalState::EvalState()
     nrAttrsets = nrOpUpdates = nrOpUpdateValuesCopied = 0;
     deepestStack = (char *) -1;
 
-    allowUnsafeEquality = getEnv("NIX_NO_UNSAFE_EQ", "") == "";
-
 #if HAVE_BOEHMGC
     static bool gcInitialised = true;
     if (gcInitialised) {
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 1db3453f39..75438f5eba 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -209,8 +209,6 @@ public:
 private:
     SrcToStore srcToStore; 
 
-    bool allowUnsafeEquality;
-
     /* A cache from path names to parse trees. */
     std::map<Path, Expr *> parseTrees;