diff --git a/pkgs/applications/networking/browsers/icecat-3/default.nix b/pkgs/applications/networking/browsers/icecat-3/default.nix
index 91a56a436ab8..9759a007de8f 100644
--- a/pkgs/applications/networking/browsers/icecat-3/default.nix
+++ b/pkgs/applications/networking/browsers/icecat-3/default.nix
@@ -20,7 +20,9 @@ stdenv.mkDerivation {
     xlibs.libXi xlibs.libX11 xlibs.libXrender xlibs.libXft xlibs.libXt
   ];
 
-  patches = [ ./skip-gre-registration.patch ./rpath-link.patch ];
+  patches = [
+    ./skip-gre-registration.patch ./rpath-link.patch ./pythonpath.patch
+  ];
 
   configureFlags = [
     "--enable-application=${application}"
diff --git a/pkgs/applications/networking/browsers/icecat-3/pythonpath.patch b/pkgs/applications/networking/browsers/icecat-3/pythonpath.patch
new file mode 100644
index 000000000000..c66800d57e57
--- /dev/null
+++ b/pkgs/applications/networking/browsers/icecat-3/pythonpath.patch
@@ -0,0 +1,14 @@
+This patch makes sure $PYTHONPATH is not overridden so that the `ply'
+Python module is visible.
+
+--- icecat-3.5.1/js/src/xpconnect/src/Makefile.in	2009-07-18 14:33:08.000000000 +0200
++++ icecat-3.5.1/js/src/xpconnect/src/Makefile.in	2009-07-20 16:31:43.000000000 +0200
+@@ -209,7 +209,7 @@ dom_quickstubs.h dom_quickstubs.cpp: $(s
+                                      $(topsrcdir)/xpcom/idl-parser/header.py \
+                                      $(topsrcdir)/xpcom/idl-parser/xpidl.py \
+                                      $(DEPTH)/js/src/mozilla-config.h
+-	PYTHONPATH=$(topsrcdir)/xpcom/idl-parser \
++	PYTHONPATH="$$PYTHONPATH:$(topsrcdir)/xpcom/idl-parser" \
+ 	  $(PYTHON) $(srcdir)/qsgen.py \
+ 	  --idlpath=$(DEPTH)/dist/idl \
+ 	  --cachedir=$(DEPTH)/xpcom/idl-parser \