diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index e92ed50fd..1410e5144 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -21,7 +21,8 @@ int cacheTerms;
 
 bool shortCircuit;
 bool closedTerms; // don't substitute under terms known to be closed
-bool substCache; // memoization of the term substitution function 
+bool substCache; // memoization of the term substitution function
+bool posInfo; // attach position info to functions, assertions, attributes
 
 #define maxActiveCalls 4096
 
@@ -43,6 +44,7 @@ EvalState::EvalState()
     strictMode = getEnv("NIX_STRICT", "0") == "1";
     closedTerms = getEnv("NIX_CLOSED_TERMS", "1") == "1";
     substCache = getEnv("NIX_SUBST_CACHE", "1") == "1";
+    posInfo = getEnv("NIX_POS_INFO", "1") == "1";
 
     ATprotectMemory(activeCalls, maxActiveCalls);
 }
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index e943bdc97..93dd653c0 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -70,11 +70,13 @@ static Expr fixAttrs(int recursive, ATermList as)
 
 void backToString(yyscan_t scanner);
 
+
+extern bool posInfo;
  
 static Pos makeCurPos(YYLTYPE * loc, ParseData * data)
 {
-    return makePos(toATerm(data->path),
-        loc->first_line, loc->first_column);
+    return posInfo ? makePos(toATerm(data->path),
+        loc->first_line, loc->first_column) : makeNoPos();
 }
 
 #define CUR_POS makeCurPos(yylocp, data)