diff --git a/scripts/nix-build.in b/scripts/nix-build.in
index 08201f8576..bce4a80078 100644
--- a/scripts/nix-build.in
+++ b/scripts/nix-build.in
@@ -122,7 +122,7 @@ foreach my $expr (@exprs) {
     close DRVPATHS or exit 1;
 
     foreach my $drvPath (@drvPaths) {
-        my $target = readlink $drvPath;
+        my $target = readlink $drvPath or die "cannot read symlink `$drvPath'";
         print STDERR "store derivation is $target\n";
     }
 
@@ -134,7 +134,7 @@ foreach my $expr (@exprs) {
     close OUTPATHS or exit 1;
 
     foreach my $outPath (@outPaths) {
-        my $target = readlink $outPath;
+        my $target = readlink $outPath or die "cannot read symlink `$outPath'";
         print "$target\n";
     }
 }
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index e04e9c1071..2ad52d8bf4 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -97,6 +97,11 @@ Path addPermRoot(const Path & _storePath, const Path & _gcRoot,
     Path gcRoot(canonPath(_gcRoot));
     assertStorePath(storePath);
 
+    if (isInStore(gcRoot))
+        throw Error(format(
+                "creating a garbage collector root (%1%) in the Nix store is forbidden "
+                "(are you running nix-build inside the store?)") % gcRoot);
+
     if (indirect) {
         createSymlink(gcRoot, storePath, true);
         store->addIndirectRoot(gcRoot);
@@ -114,7 +119,6 @@ Path addPermRoot(const Path & _storePath, const Path & _gcRoot,
         }
             
         createSymlink(gcRoot, storePath, false);
-
     }
 
     /* Check that the root can be found by the garbage collector. */