diff --git a/src/libstore/derivations.cc b/src/libstore/derivations.cc
index eea129df3..106ec5daa 100644
--- a/src/libstore/derivations.cc
+++ b/src/libstore/derivations.cc
@@ -468,10 +468,7 @@ static const DrvHashModulo & pathDerivationModulo(Store & store, const StorePath
             drvPath,
             hashDerivationModulo(
                 store,
-                parseDerivation(
-                    store,
-                    readFile(store.toRealPath(drvPath)),
-                    Derivation::nameFromPath(drvPath)),
+                store.readInvalidDerivation(drvPath),
                 false)).first;
     }
     return h->second;
diff --git a/src/libstore/local-store.cc b/src/libstore/local-store.cc
index e4e404dca..93d073768 100644
--- a/src/libstore/local-store.cc
+++ b/src/libstore/local-store.cc
@@ -624,10 +624,7 @@ uint64_t LocalStore::addValidPath(State & state,
        efficiently query whether a path is an output of some
        derivation. */
     if (info.path.isDerivation()) {
-        auto drv = parseDerivation(
-            *this,
-            readFile(Store::toRealPath(info.path)),
-            Derivation::nameFromPath(info.path));
+        auto drv = readInvalidDerivation(info.path);
 
         /* Verify that the output paths in the derivation are correct
            (i.e., follow the scheme for computing output paths from
@@ -1003,10 +1000,7 @@ void LocalStore::registerValidPaths(const ValidPathInfos & infos)
             if (i.path.isDerivation()) {
                 // FIXME: inefficient; we already loaded the derivation in addValidPath().
                 checkDerivationOutputs(i.path,
-                    parseDerivation(
-                        *this,
-                        readFile(Store::toRealPath(i.path)),
-                        Derivation::nameFromPath(i.path)));
+                    readInvalidDerivation(i.path));
             }
 
         /* Do a topological sort of the paths.  This will throw an
diff --git a/src/libstore/store-api.cc b/src/libstore/store-api.cc
index 83d3a1fa1..7f808f45a 100644
--- a/src/libstore/store-api.cc
+++ b/src/libstore/store-api.cc
@@ -1007,6 +1007,14 @@ Derivation Store::readDerivation(const StorePath & drvPath)
     }
 }
 
+Derivation Store::readInvalidDerivation(const StorePath & drvPath)
+{
+    return parseDerivation(
+        *this,
+        readFile(Store::toRealPath(drvPath)),
+        Derivation::nameFromPath(drvPath));
+}
+
 }
 
 
diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index f77bc21d1..30c9e7d0a 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -611,6 +611,9 @@ public:
     /* Read a derivation (which must already be valid). */
     Derivation readDerivation(const StorePath & drvPath);
 
+    /* Read a derivation from a potentially invalid path. */
+    Derivation readInvalidDerivation(const StorePath & drvPath);
+
     /* Place in `out' the set of all store paths in the file system
        closure of `storePath'; that is, all paths than can be directly
        or indirectly reached from it.  `out' is not cleared.  If