diff --git a/src/libcmd/repl.cc b/src/libcmd/repl.cc
index 9002fa555..c7fd0db91 100644
--- a/src/libcmd/repl.cc
+++ b/src/libcmd/repl.cc
@@ -594,8 +594,8 @@ bool NixRepl::processLine(std::string line)
                 return {path, 0};
             } else if (v.isLambda()) {
                 auto pos = state->positions[v.lambda.fun->pos];
-                if (auto path = std::get_if<Path>(&pos.origin))
-                    return {SourcePath(CanonPath(*path)), pos.line};
+                if (auto path = std::get_if<SourcePath>(&pos.origin))
+                    return {*path, pos.line};
                 else
                     throw Error("'%s' cannot be shown in an editor", pos);
             } else {
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index 3b2877602..dec123b69 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -499,6 +499,7 @@ EvalState::EvalState(
     , sOutputSpecified(symbols.create("outputSpecified"))
     , repair(NoRepair)
     , emptyBindings(0)
+    , derivationInternal(rootPath(CanonPath("/builtin/derivation.nix")))
     , store(store)
     , buildStore(buildStore ? buildStore : store)
     , debugRepl(nullptr)
@@ -991,9 +992,9 @@ void EvalState::mkThunk_(Value & v, Expr * expr)
 void EvalState::mkPos(Value & v, PosIdx p)
 {
     auto pos = positions[p];
-    if (auto path = std::get_if<Path>(&pos.origin)) {
+    if (auto path = std::get_if<SourcePath>(&pos.origin)) {
         auto attrs = buildBindings(3);
-        attrs.alloc(sFile).mkString(*path);
+        attrs.alloc(sFile).mkString(path->path.abs());
         attrs.alloc(sLine).mkInt(pos.line);
         attrs.alloc(sColumn).mkInt(pos.column);
         v.mkAttrs(attrs);
@@ -1373,8 +1374,8 @@ void ExprSelect::eval(EvalState & state, Env & env, Value & v)
     } catch (Error & e) {
         if (pos2) {
             auto pos2r = state.positions[pos2];
-            auto origin = std::get_if<Path>(&pos2r.origin);
-            if (!(origin && *origin == state.derivationNixPath))
+            auto origin = std::get_if<SourcePath>(&pos2r.origin);
+            if (!(origin && *origin == state.derivationInternal))
                 state.addErrorTrace(e, pos2, "while evaluating the attribute '%1%'",
                     showAttrPath(state, env, attrPath));
         }
@@ -2417,8 +2418,8 @@ void EvalState::printStats()
                     else
                         obj["name"] = nullptr;
                     if (auto pos = positions[fun->pos]) {
-                        if (auto path = std::get_if<Path>(&pos.origin))
-                            obj["file"] = *path;
+                        if (auto path = std::get_if<SourcePath>(&pos.origin))
+                            obj["file"] = path->to_string();
                         obj["line"] = pos.line;
                         obj["column"] = pos.column;
                     }
@@ -2432,8 +2433,8 @@ void EvalState::printStats()
                 for (auto & i : attrSelects) {
                     json obj = json::object();
                     if (auto pos = positions[i.first]) {
-                        if (auto path = std::get_if<Path>(&pos.origin))
-                            obj["file"] = *path;
+                        if (auto path = std::get_if<SourcePath>(&pos.origin))
+                            obj["file"] = path->to_string();
                         obj["line"] = pos.line;
                         obj["column"] = pos.column;
                     }
diff --git a/src/libexpr/eval.hh b/src/libexpr/eval.hh
index 1e8f8391c..b9578321f 100644
--- a/src/libexpr/eval.hh
+++ b/src/libexpr/eval.hh
@@ -127,8 +127,6 @@ public:
     SymbolTable symbols;
     PosTable positions;
 
-    static inline std::string derivationNixPath = "//builtin/derivation.nix";
-
     const Symbol sWith, sOutPath, sDrvPath, sType, sMeta, sName, sValue,
         sSystem, sOverrides, sOutputs, sOutputName, sIgnoreNulls,
         sFile, sLine, sColumn, sFunctor, sToString,
@@ -139,7 +137,6 @@ public:
         sDescription, sSelf, sEpsilon, sStartSet, sOperator, sKey, sPath,
         sPrefix,
         sOutputSpecified;
-    Symbol sDerivationNix;
 
     /* If set, force copying files to the Nix store even if they
        already exist there. */
@@ -151,6 +148,8 @@ public:
 
     Bindings emptyBindings;
 
+    const SourcePath derivationInternal;
+
     /* Store used to materialise .drv files. */
     const ref<Store> store;
 
diff --git a/src/libexpr/flake/flake.cc b/src/libexpr/flake/flake.cc
index 2b858ee98..4c571fd7d 100644
--- a/src/libexpr/flake/flake.cc
+++ b/src/libexpr/flake/flake.cc
@@ -220,7 +220,7 @@ static Flake getFlake(
     Value vInfo;
     state.evalFile(CanonPath(flakeFile), vInfo, true); // FIXME: symlink attack
 
-    expectType(state, nAttrs, vInfo, state.positions.add({flakeFile}, 1, 1));
+    expectType(state, nAttrs, vInfo, state.positions.add({CanonPath(flakeFile)}, 1, 1));
 
     if (auto description = vInfo.attrs->get(state.sDescription)) {
         expectType(state, nString, *description->value, description->pos);
diff --git a/src/libexpr/nixexpr.cc b/src/libexpr/nixexpr.cc
index eb6f062b4..2c9d5754e 100644
--- a/src/libexpr/nixexpr.cc
+++ b/src/libexpr/nixexpr.cc
@@ -31,9 +31,9 @@ struct PosAdapter : AbstractPos
                 // Get rid of the null terminators added by the parser.
                 return std::string(s.source->c_str());
             },
-            [](const Path & path) -> std::optional<std::string> {
+            [](const SourcePath & path) -> std::optional<std::string> {
                 try {
-                    return readFile(path);
+                    return path.readFile();
                 } catch (Error &) {
                     return std::nullopt;
                 }
@@ -47,7 +47,7 @@ struct PosAdapter : AbstractPos
             [&](const Pos::none_tag &) { out << "«none»"; },
             [&](const Pos::Stdin &) { out << "«stdin»"; },
             [&](const Pos::String & s) { out << "«string»"; },
-            [&](const Path & path) { out << path; }
+            [&](const SourcePath & path) { out << path; }
         }, origin);
     }
 };
diff --git a/src/libexpr/nixexpr.hh b/src/libexpr/nixexpr.hh
index 4079a7b24..d70280582 100644
--- a/src/libexpr/nixexpr.hh
+++ b/src/libexpr/nixexpr.hh
@@ -32,7 +32,7 @@ struct Pos
     struct Stdin { ref<std::string> source; };
     struct String { ref<std::string> source; };
 
-    typedef std::variant<none_tag, Stdin, String, Path> Origin;
+    typedef std::variant<none_tag, Stdin, String, SourcePath> Origin;
 
     Origin origin;
 
diff --git a/src/libexpr/parser.y b/src/libexpr/parser.y
index 8b67665db..4d981712a 100644
--- a/src/libexpr/parser.y
+++ b/src/libexpr/parser.y
@@ -700,7 +700,7 @@ Expr * EvalState::parseExprFromFile(const SourcePath & path, std::shared_ptr<Sta
     auto buffer = path.readFile();
     // readFile hopefully have left some extra space for terminators
     buffer.append("\0\0", 2);
-    return parse(buffer.data(), buffer.size(), path.path.abs(), path.parent(), staticEnv);
+    return parse(buffer.data(), buffer.size(), Pos::Origin(path), path.parent(), staticEnv);
 }
 
 
diff --git a/src/libexpr/primops.cc b/src/libexpr/primops.cc
index c77d45bd3..7c34e93ad 100644
--- a/src/libexpr/primops.cc
+++ b/src/libexpr/primops.cc
@@ -4136,7 +4136,6 @@ void EvalState::createBaseEnv()
 
     /* Add a wrapper around the derivation primop that computes the
        `drvPath' and `outPath' attributes lazily. */
-    sDerivationNix = symbols.create(derivationNixPath);
     auto vDerivation = allocValue();
     addConstant("derivation", vDerivation);
 
@@ -4153,7 +4152,7 @@ void EvalState::createBaseEnv()
         // the parser needs two NUL bytes as terminators; one of them
         // is implied by being a C string.
         "\0";
-    eval(parse(code, sizeof(code), derivationNixPath, {CanonPath::root}, staticBaseEnv), *vDerivation);
+    eval(parse(code, sizeof(code), derivationInternal, {CanonPath::root}, staticBaseEnv), *vDerivation);
 }
 
 
diff --git a/src/libexpr/value-to-xml.cc b/src/libexpr/value-to-xml.cc
index a9fcb803e..4e87ac4b6 100644
--- a/src/libexpr/value-to-xml.cc
+++ b/src/libexpr/value-to-xml.cc
@@ -24,8 +24,8 @@ static void printValueAsXML(EvalState & state, bool strict, bool location,
 
 static void posToXML(EvalState & state, XMLAttrs & xmlAttrs, const Pos & pos)
 {
-    if (auto path = std::get_if<Path>(&pos.origin))
-        xmlAttrs["path"] = *path;
+    if (auto path = std::get_if<SourcePath>(&pos.origin))
+        xmlAttrs["path"] = path->path.abs();
     xmlAttrs["line"] = fmt("%1%", pos.line);
     xmlAttrs["column"] = fmt("%1%", pos.column);
 }