diff --git a/scripts/nix-push.in b/scripts/nix-push.in
index 800424c896..85b74b84cc 100644
--- a/scripts/nix-push.in
+++ b/scripts/nix-push.in
@@ -86,6 +86,12 @@ foreach my $storePath (@storePaths) {
     die unless ($storePath =~ /\/[0-9a-z]{32}.*$/);
 
     # Construct a Nix expression that creates a Nix archive.
+    # !!! the string reference to `$storePath' is impure!  We could
+    # also pass it as a normal input, but that would cause it to be
+    # copied, and its name would be expanded (e.g.,
+    # /nix/store/HASH1-HASH2-symname).  nix-instantiate should be
+    # smart enough to add store paths as direct references of the Nix
+    # expression.
     my $nixexpr = 
         "((import $dataDir/nix/corepkgs/nar/nar.nix) " .
         "{path = \"$storePath\"; system = \"@system@\"; hashAlgo = \"$hashAlgo\";}) ";
@@ -122,7 +128,11 @@ while (scalar @tmp > 0) {
     my @tmp2 = @tmp[0..$n - 1];
     @tmp = @tmp[$n..scalar @tmp - 1];
 
-    my $pid = open(READ, "$binDir/nix-store --realise @tmp2|")
+    # Note: we disable build hooks because of the impure path
+    # reference (see above).  Even if that is fixed, using a hook
+    # probably wouldn't make that much sense; pumping lots of data
+    # around just to compress them won't gain that much.
+    my $pid = open(READ, "NIX_BUILD_HOOK= $binDir/nix-store --realise @tmp2|")
         or die "cannot run nix-store";
     while (<READ>) {
         chomp;
diff --git a/src/libexpr/Makefile.am b/src/libexpr/Makefile.am
index 5571179f8f..dbc93abd5e 100644
--- a/src/libexpr/Makefile.am
+++ b/src/libexpr/Makefile.am
@@ -15,7 +15,7 @@ AM_CFLAGS = \
 
 # Parser generation.
 
-parser.o: parser-tab.h lexer-tab.h
+parser.cc: parser-tab.h lexer-tab.h
 
 parser-tab.c parser-tab.h: parser.y
 	$(bison) -v -o parser-tab.c parser.y -d