diff --git a/docs/grub.texi b/docs/grub.texi
index 5ac61c09d..d788efe44 100644
--- a/docs/grub.texi
+++ b/docs/grub.texi
@@ -1495,7 +1495,7 @@ Normally, @command{grub-mkconfig} will generate top level menu entry for
 the kernel with highest version number and put all other found kernels
 or alternative menu entries for recovery mode in submenu. For entries returned
 by @command{os-prober} first entry will be put on top level and all others
-in submenu. If this option is set to @samp{y}, flat menu with all entries
+in submenu. If this option is set to @samp{true}, flat menu with all entries
 on top level will be generated instead. Changing this option will require
 changing existing values of @samp{GRUB_DEFAULT}, @samp{fallback} (@pxref{fallback})
 and @samp{default} (@pxref{default}) environment variables as well as saved
diff --git a/util/grub.d/10_hurd.in b/util/grub.d/10_hurd.in
index 59a9a48a2..3663d360e 100644
--- a/util/grub.d/10_hurd.in
+++ b/util/grub.d/10_hurd.in
@@ -156,7 +156,15 @@ is_top_level=true
 while [ "x$kernels" != "x" ] ; do
   kernel=`version_find_latest $kernels`
 
-  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+  # The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+  # mentioned in the documentation that has to be set to 'y' instead of 'true' to
+  # enable it. This caused a lot of confusion to users that set the option to 'y',
+  # 'yes' or 'true'. This was fixed but all of these values must be supported now.
+  if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+      GRUB_DISABLE_SUBMENU="true"
+  fi
+
+  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
       hurd_entry "$kernel" simple
       submenu_indentation="$grub_tab"
     
diff --git a/util/grub.d/10_kfreebsd.in b/util/grub.d/10_kfreebsd.in
index 9d8e8fd85..199b20e16 100644
--- a/util/grub.d/10_kfreebsd.in
+++ b/util/grub.d/10_kfreebsd.in
@@ -214,7 +214,15 @@ while [ "x$list" != "x" ] ; do
     module_dir_rel=$(make_system_path_relative_to_its_root $module_dir)
   fi
 
-  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+  # The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+  # mentioned in the documentation that has to be set to 'y' instead of 'true' to
+  # enable it. This caused a lot of confusion to users that set the option to 'y',
+  # 'yes' or 'true'. This was fixed but all of these values must be supported now.
+  if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+      GRUB_DISABLE_SUBMENU="true"
+  fi
+
+  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
       kfreebsd_entry "${OS}" "${version}" simple
       submenu_indentation="$grub_tab"
     
diff --git a/util/grub.d/10_linux.in b/util/grub.d/10_linux.in
index 4532266be..e8b01c0d0 100644
--- a/util/grub.d/10_linux.in
+++ b/util/grub.d/10_linux.in
@@ -261,7 +261,15 @@ while [ "x$list" != "x" ] ; do
     fi
   fi
 
-  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+  # The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+  # mentioned in the documentation that has to be set to 'y' instead of 'true' to
+  # enable it. This caused a lot of confusion to users that set the option to 'y',
+  # 'yes' or 'true'. This was fixed but all of these values must be supported now.
+  if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+    GRUB_DISABLE_SUBMENU="true"
+  fi
+
+  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
     linux_entry "${OS}" "${version}" simple \
     "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}"
 
diff --git a/util/grub.d/10_netbsd.in b/util/grub.d/10_netbsd.in
index 874f59969..dc0cd1b17 100644
--- a/util/grub.d/10_netbsd.in
+++ b/util/grub.d/10_netbsd.in
@@ -157,7 +157,15 @@ for k in /netbsd $(ls -t /netbsd?* 2>/dev/null) ; do
 
   gettext_printf "Found NetBSD kernel: %s\n" "$k" >&2
 
-  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+  # The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+  # mentioned in the documentation that has to be set to 'y' instead of 'true' to
+  # enable it. This caused a lot of confusion to users that set the option to 'y',
+  # 'yes' or 'true'. This was fixed but all of these values must be supported now.
+  if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+    GRUB_DISABLE_SUBMENU="true"
+  fi
+
+  if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
       netbsd_entry "knetbsd"   "$k" simple "${GRUB_CMDLINE_NETBSD_DEFAULT}"
     submenu_indentation="$grub_tab"
     
diff --git a/util/grub.d/20_linux_xen.in b/util/grub.d/20_linux_xen.in
index 96179ea61..391942a59 100644
--- a/util/grub.d/20_linux_xen.in
+++ b/util/grub.d/20_linux_xen.in
@@ -288,7 +288,15 @@ while [ "x${xen_list}" != "x" ] ; do
 	    fi
 	fi
 
-	if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+	# The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+	# mentioned in the documentation that has to be set to 'y' instead of 'true' to
+	# enable it. This caused a lot of confusion to users that set the option to 'y',
+	# 'yes' or 'true'. This was fixed but all of these values must be supported now.
+	if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+	    GRUB_DISABLE_SUBMENU="true"
+	fi
+
+	if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
 	    linux_entry "${OS}" "${version}" "${xen_version}" simple \
 		"${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" "${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT}"
 
diff --git a/util/grub.d/30_os-prober.in b/util/grub.d/30_os-prober.in
index 515a68c7a..cf42f55e8 100644
--- a/util/grub.d/30_os-prober.in
+++ b/util/grub.d/30_os-prober.in
@@ -234,7 +234,15 @@ EOF
 	  prepare_boot_cache="$(prepare_grub_to_access_device ${LBOOT} | grub_add_tab)"
 	fi
 
-	if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
+	# The GRUB_DISABLE_SUBMENU option used to be different than others since it was
+	# mentioned in the documentation that has to be set to 'y' instead of 'true' to
+	# enable it. This caused a lot of confusion to users that set the option to 'y',
+	# 'yes' or 'true'. This was fixed but all of these values must be supported now.
+	if [ "x${GRUB_DISABLE_SUBMENU}" = xyes ] || [ "x${GRUB_DISABLE_SUBMENU}" = xy ]; then
+	    GRUB_DISABLE_SUBMENU="true"
+	fi
+
+	if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xtrue ]; then
             cat << EOF
 menuentry '$(echo "$OS $onstr" | grub_quote)' $CLASS --class gnu-linux --class gnu --class os \$menuentry_id_option 'osprober-gnulinux-simple-$boot_device_id' {
 EOF