diff --git a/gtk/gtkwin32.c b/gtk/gtkwin32.c
index b582942a7e..e9ba709d87 100644
--- a/gtk/gtkwin32.c
+++ b/gtk/gtkwin32.c
@@ -59,7 +59,8 @@ _gtk_get_libdir (void)
     {
       gchar *root = g_win32_get_package_installation_directory_of_module (gtk_dll);
       gchar *slash = strrchr (root, '\\');
-      if (g_ascii_strcasecmp (slash + 1, ".libs") == 0)
+      if (slash != NULL &&
+          g_ascii_strcasecmp (slash + 1, ".libs") == 0)
         gtk_libdir = GTK_LIBDIR;
       else
         gtk_libdir = g_build_filename (root, "lib", NULL);