diff --git a/cmake/gtk.cmake b/cmake/gtk.cmake
index 85ecb7de..34396d2f 100644
--- a/cmake/gtk.cmake
+++ b/cmake/gtk.cmake
@@ -3,7 +3,7 @@
 set(PUTTY_GTK_VERSION "ANY"
   CACHE STRING "Which major version of GTK to build with")
 set_property(CACHE PUTTY_GTK_VERSION
-  PROPERTY STRINGS ANY 3 2 1)
+  PROPERTY STRINGS ANY 3 2 1 NONE)
 
 set(GTK_FOUND FALSE)
 
diff --git a/cmake/platforms/unix.cmake b/cmake/platforms/unix.cmake
index 95339f22..04db8129 100644
--- a/cmake/platforms/unix.cmake
+++ b/cmake/platforms/unix.cmake
@@ -65,21 +65,23 @@ endif()
 
 include(cmake/gtk.cmake)
 
-# See if we have X11 available. This requires libX11 itself, and also
-# the GDK integration to X11.
-find_package(X11)
+if(GTK_FOUND)
+  # See if we have X11 available. This requires libX11 itself, and also
+  # the GDK integration to X11.
+  find_package(X11)
 
-function(check_x11)
-  list(APPEND CMAKE_REQUIRED_INCLUDES ${GTK_INCLUDE_DIRS})
-  check_include_file(gdk/gdkx.h HAVE_GDK_GDKX_H)
+  function(check_x11)
+    list(APPEND CMAKE_REQUIRED_INCLUDES ${GTK_INCLUDE_DIRS})
+    check_include_file(gdk/gdkx.h HAVE_GDK_GDKX_H)
 
-  if(X11_FOUND AND HAVE_GDK_GDKX_H)
-    set(NOT_X_WINDOWS OFF PARENT_SCOPE)
-  else()
-    set(NOT_X_WINDOWS ON PARENT_SCOPE)
-  endif()
-endfunction()
-check_x11()
+    if(X11_FOUND AND HAVE_GDK_GDKX_H)
+      set(NOT_X_WINDOWS OFF PARENT_SCOPE)
+    else()
+      set(NOT_X_WINDOWS ON PARENT_SCOPE)
+    endif()
+  endfunction()
+  check_x11()
+endif()
 
 include_directories(${CMAKE_SOURCE_DIR}/charset ${GTK_INCLUDE_DIRS} ${X11_INCLUDE_DIR})
 link_directories(${GTK_LIBRARY_DIRS})