diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1f55c9c72d..bfe3b2b6f5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 ### Changed
  - Changed flexible array definitions in public I/O interface headers to not
    use "1" as the number of array elements.
+ - The minimum supported OCaml toolchain version is now 4.05
  - On x86:
    - HVM PIRQs are disabled by default.
    - Reduce IOMMU setup time for hardware domain.
diff --git a/tools/configure b/tools/configure
index 0135a0059a..3d557234b3 100755
--- a/tools/configure
+++ b/tools/configure
@@ -6836,7 +6836,7 @@ else
                      -e 's/[^0-9]//g'`
 
 
-  ax_compare_version_B=`echo "4.02.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
+  ax_compare_version_B=`echo "4.05.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
                      -e 's/Z\([0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9][0-9]\)Z/Z0\1Z/g' \
diff --git a/tools/configure.ac b/tools/configure.ac
index 618ef8c63f..851887080c 100644
--- a/tools/configure.ac
+++ b/tools/configure.ac
@@ -336,7 +336,7 @@ AS_IF([test "x$ocamltools" = "xy"], [
             AC_MSG_ERROR([Ocaml tools enabled, but missing ocamlopt or ocamlfind])])
         ocamltools="n"
     ], [
-        AX_COMPARE_VERSION([$OCAMLVERSION], [lt], [4.02.0], [
+        AX_COMPARE_VERSION([$OCAMLVERSION], [lt], [4.05.0], [
             AS_IF([test "x$enable_ocamltools" = "xyes"], [
                 AC_MSG_ERROR([Your version of OCaml: $OCAMLVERSION is not supported])])
             ocamltools="n"
diff --git a/tools/ocaml/xenstored/disk.ml b/tools/ocaml/xenstored/disk.ml
index 91f945f2bd..ccaa048faf 100644
--- a/tools/ocaml/xenstored/disk.ml
+++ b/tools/ocaml/xenstored/disk.ml
@@ -30,7 +30,7 @@ let undec c =
   | _          -> raise (Failure "undecify")
 
 let unhex c =
-  let c = Char.lowercase c in
+  let c = Char.lowercase_ascii c in
   match c with
   | '0' .. '9' -> (Char.code c) - (Char.code '0')
   | 'a' .. 'f' -> (Char.code c) - (Char.code 'a') + 10