diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
index 9a9531a3f..b8eef9286 100644
--- a/src/libexpr/attr-path.cc
+++ b/src/libexpr/attr-path.cc
@@ -121,7 +121,7 @@ Pos findDerivationFilename(EvalState & state, Value & v, std::string what)
 
     Symbol file = state.symbols.create(filename);
 
-    return { file, lineno, 0 };
+    return { foFile, file, lineno, 0 };
 }
 
 
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 1485dc7fe..8471c2f8b 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -249,7 +249,7 @@ private:
     friend struct ExprAttrs;
     friend struct ExprLet;
 
-    Expr * parse(const char * text, const Path & path,
+    Expr * parse(const char * text, FileOrigin origin, const Path & path,
         const Path & basePath, StaticEnv & staticEnv);
 
 public:
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 47d0e85ec..5a98b9149 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -24,11 +24,12 @@ MakeError(RestrictedPathError, Error);
 
 struct Pos
 {
+    FileOrigin origin;
     Symbol file;
     unsigned int line, column;
-    Pos() : line(0), column(0) { };
-    Pos(const Symbol & file, unsigned int line, unsigned int column)
-        : file(file), line(line), column(column) { };
+    Pos() : origin(foString), line(0), column(0) { };
+    Pos(FileOrigin origin, const Symbol & file, unsigned int line, unsigned int column)
+        : origin(origin), file(file), line(line), column(column) { };
     operator bool() const
     {
         return line != 0;
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 0417a3c21..1a4f3d56b 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -30,7 +30,8 @@ namespace nix {
         SymbolTable & symbols;
         Expr * result;
         Path basePath;
-        Symbol path;
+        Symbol file;
+        FileOrigin origin;
         ErrorInfo error;
         Symbol sLetBody;
         ParseData(EvalState & state)
@@ -250,7 +251,7 @@ static Expr * stripIndentation(const Pos & pos, SymbolTable & symbols, vector<Ex
 
 static inline Pos makeCurPos(const YYLTYPE & loc, ParseData * data)
 {
-    return Pos(data->path, loc.first_line, loc.first_column);
+    return Pos(data->origin, data->file, loc.first_line, loc.first_column);
 }
 
 #define CUR_POS makeCurPos(*yylocp, data)
@@ -576,13 +577,24 @@ formal
 namespace nix {
 
 
-Expr * EvalState::parse(const char * text,
+Expr * EvalState::parse(const char * text, FileOrigin origin,
     const Path & path, const Path & basePath, StaticEnv & staticEnv)
 {
     yyscan_t scanner;
     ParseData data(*this);
+    data.origin = origin;
+    switch (origin) {
+        case foFile: 
+            data.file = data.symbols.create(path);
+            break;
+        case foStdin:
+        case foString:
+            data.file = data.symbols.create(text);
+            break;
+        default:
+            throw Error("invalid FileOrigin in parse");
+    }
     data.basePath = basePath;
-    data.path = data.symbols.create(path);
 
     yylex_init(&scanner);
     yy_scan_string(text, scanner);
@@ -632,13 +644,13 @@ Expr * EvalState::parseExprFromFile(const Path & path)
 
 Expr * EvalState::parseExprFromFile(const Path & path, StaticEnv & staticEnv)
 {
-    return parse(readFile(path).c_str(), path, dirOf(path), staticEnv);
+    return parse(readFile(path).c_str(), foFile, path, dirOf(path), staticEnv);
 }
 
 
 Expr * EvalState::parseExprFromString(std::string_view s, const Path & basePath, StaticEnv & staticEnv)
 {
-    return parse(s.data(), "(string)", basePath, staticEnv);
+    return parse(s.data(), foString, "", basePath, staticEnv);
 }
 
 
@@ -651,7 +663,8 @@ Expr * EvalState::parseExprFromString(std::string_view s, const Path & basePath)
 Expr * EvalState::parseStdin()
 {
     //Activity act(*logger, lvlTalkative, format("parsing standard input"));
-    return parseExprFromString(drainFD(0), absPath("."));
+    // return parseExprFromString(foStdin, drainFD(0), absPath("."));
+    return parse(drainFD(0).data(), foStdin, "", absPath("."), staticBaseEnv);
 }
 
 
diff --git a/src/libutil/error.cc b/src/libutil/error.cc
index 7aff9381b..ee415e18c 100644
--- a/src/libutil/error.cc
+++ b/src/libutil/error.cc
@@ -59,22 +59,51 @@ void getCodeLines(NixCode &nixCode)
         return;
 
     // check this magic value!
-    if (nixCode.errPos.file == "(string)")
-        return;
-
-    try {
-        AutoCloseFD fd = open(nixCode.errPos.file.c_str(), O_RDONLY | O_CLOEXEC);
-        if (!fd)
-            throw SysError("opening file '%1%'", nixCode.errPos.file);
+    if (nixCode.errPos.origin == foFile) {
+        try {
+            AutoCloseFD fd = open(nixCode.errPos.file.c_str(), O_RDONLY | O_CLOEXEC);
+            if (!fd)
+                throw SysError("opening file '%1%'", nixCode.errPos.file);
 
+            // count the newlines.
+            int count = 0;
+            string line;
+            int pl = nixCode.errPos.line - 1;
+            do 
+            {
+                line = readLine(fd.get());
+                ++count;
+                if (count < pl) 
+                {
+                  ;
+                }
+                else if (count == pl) {
+                    nixCode.prevLineOfCode = line;
+                } else if (count == pl + 1) {
+                    nixCode.errLineOfCode = line;
+                } else if (count == pl + 2) {
+                    nixCode.nextLineOfCode = line;
+                    break;
+                }
+            } while (true);
+        }
+        catch (EndOfFile &eof) {
+            ;
+        }
+        catch (std::exception &e) {
+            printError("error reading nix file: %s\n%s", nixCode.errPos.file, e.what());
+        }
+    } else { 
+        std::istringstream iss(nixCode.errPos.file);
         // count the newlines.
-        
         int count = 0;
         string line;
         int pl = nixCode.errPos.line - 1;
+
         do 
         {
-            line = readLine(fd.get());
+            std::getline(iss, line);
+            // std::cout << "getline result: " << std::getline(iss, line) << std::endl;
             ++count;
             if (count < pl) 
             {
@@ -88,14 +117,11 @@ void getCodeLines(NixCode &nixCode)
                 nixCode.nextLineOfCode = line;
                 break;
             }
+
+            if (!iss.good())
+                break;
         } while (true);
     }
-    catch (EndOfFile &eof) {
-        ;
-    }
-    catch (std::exception &e) {
-        printError("error reading nix file: %s\n%s", nixCode.errPos.file, e.what());
-    }
 }
 
 
@@ -225,15 +251,27 @@ std::ostream& operator<<(std::ostream &out, const ErrorInfo &einfo)
 
     // filename, line, column.
     if (einfo.nixCode.has_value()) {
-        if (einfo.nixCode->errPos.file != "") {
-            out << fmt("%1%in file: " ANSI_BLUE "%2% %3%" ANSI_NORMAL,
-                prefix,
-                einfo.nixCode->errPos.file,
-                showErrPos(einfo.nixCode->errPos)) << std::endl;
-            out << prefix << std::endl;
-        } else {
-            out << fmt("%1%from command line argument", prefix) << std::endl;
-            out << prefix << std::endl;
+        switch (einfo.nixCode->errPos.origin) {
+            case foFile: {
+                out << fmt("%1%in file: " ANSI_BLUE "%2% %3%" ANSI_NORMAL,
+                    prefix,
+                    einfo.nixCode->errPos.file,
+                    showErrPos(einfo.nixCode->errPos)) << std::endl;
+                out << prefix << std::endl;
+                break;
+            }
+            case foString: {
+                out << fmt("%1%from command line argument", prefix) << std::endl;
+                out << prefix << std::endl;
+                break;
+            }
+            case foStdin: {
+                out << fmt("%1%from stdin", prefix) << std::endl;
+                out << prefix << std::endl;
+                break;
+            }
+            default:
+                throw Error("invalid FileOrigin in errPos");
         }
     }
 
diff --git a/src/libutil/error.hh b/src/libutil/error.hh
index b374c2780..d60c0fefe 100644
--- a/src/libutil/error.hh
+++ b/src/libutil/error.hh
@@ -32,10 +32,18 @@ typedef enum {
     lvlVomit
 } Verbosity;
 
+typedef enum { 
+    foFile,
+    foStdin,
+    foString
+} FileOrigin;
+
+
 struct ErrPos {
     int line = 0;
     int column = 0;
     string file;
+    FileOrigin origin;
 
     operator bool() const
     {
@@ -45,6 +53,7 @@ struct ErrPos {
     template <class P>
     ErrPos& operator=(const P &pos)
     {
+        origin = pos.origin;
         line = pos.line;
         column = pos.column;
         file = pos.file;