diff --git a/common b/common
index 9293e5eb5..4b0f1890a 160000
--- a/common
+++ b/common
@@ -1 +1 @@
-Subproject commit 9293e5eb5b8f7a8c596cc6f7701c6bbc3bd86f25
+Subproject commit 4b0f1890a41444fdacc71e418e56f6d78b46aa26
diff --git a/daemon/utils.ml b/daemon/utils.ml
index 3b5c957cf..a1d80bbc5 100644
--- a/daemon/utils.ml
+++ b/daemon/utils.ml
@@ -188,11 +188,6 @@ and compare_device_names a b =
     )
   )
 
-(* Bytes.get_uint8 was added in OCaml 4.08, so when we depend on
- * that version, remove this definition.
- *)
-external bytes_get_uint8 : bytes -> int -> int = "%bytes_safe_get"
-
 let has_bogus_mbr device =
   try
     with_openfile device [O_RDONLY; O_CLOEXEC] 0 (fun fd ->
@@ -207,7 +202,7 @@ let has_bogus_mbr device =
                        0x0E  (* FAT16B LBA *)] in
       let sec0 = Bytes.create sec0size in
       let sec0read = read fd sec0 0 sec0size in
-      let sec0at = bytes_get_uint8 sec0 in
+      let sec0at = Bytes.get_uint8 sec0 in
 
       (* sector read completely *)
       sec0read = sec0size &&
diff --git a/docs/guestfs-building.pod b/docs/guestfs-building.pod
index aef716ffc..9d97dd778 100644
--- a/docs/guestfs-building.pod
+++ b/docs/guestfs-building.pod
@@ -119,7 +119,7 @@ virt tools which are still written in Perl.
 
 I<Required>.  Part of Perl core.
 
-=item OCaml E<ge> 4.07
+=item OCaml E<ge> 4.08
 
 =item OCaml findlib
 
diff --git a/m4/guestfs-ocaml.m4 b/m4/guestfs-ocaml.m4
index bc613ac37..60233d16d 100644
--- a/m4/guestfs-ocaml.m4
+++ b/m4/guestfs-ocaml.m4
@@ -38,10 +38,10 @@ AC_ARG_ENABLE([ocaml],
     [],
     [enable_ocaml=yes])
 
-dnl OCaml >= 4.07 is required.
-ocaml_ver_str=4.07
+dnl OCaml >= 4.08 is required.
+ocaml_ver_str=4.08
 ocaml_min_major=4
-ocaml_min_minor=7
+ocaml_min_minor=8
 AC_MSG_CHECKING([if OCaml version >= $ocaml_ver_str])
 ocaml_major="`echo $OCAMLVERSION | $AWK -F. '{print $1}'`"
 ocaml_minor="`echo $OCAMLVERSION | $AWK -F. '{print $2}' | sed 's/^0//'`"
@@ -190,21 +190,6 @@ fi
 AM_CONDITIONAL([HAVE_OCAML_PKG_OUNIT],
                [test "x$OCAML_PKG_ounit2" != "xno" && test "x$ounit_is_v2" != "xno"])
 
-dnl Check if OCaml has caml_alloc_initialized_string (added 2017).
-AC_MSG_CHECKING([for caml_alloc_initialized_string])
-cat >conftest.c <<'EOF'
-#include <caml/alloc.h>
-int main () { char *p = (void *) caml_alloc_initialized_string; return 0; }
-EOF
-AS_IF([$OCAMLC conftest.c >&AS_MESSAGE_LOG_FD 2>&1],[
-    AC_MSG_RESULT([yes])
-    AC_DEFINE([HAVE_CAML_ALLOC_INITIALIZED_STRING],[1],
-              [caml_alloc_initialized_string found at compile time.])
-],[
-    AC_MSG_RESULT([no])
-])
-rm -f conftest.c conftest.o
-
 dnl Flags we want to pass to every OCaml compiler call.
 OCAML_WARN_ERROR="-warn-error +C+D+E+F+L+M+P+S+U+V+Y+Z+X+52-3-6 -w -6"
 AC_SUBST([OCAML_WARN_ERROR])
diff --git a/ocaml/guestfs-c.h b/ocaml/guestfs-c.h
index 833221aa5..44d8787da 100644
--- a/ocaml/guestfs-c.h
+++ b/ocaml/guestfs-c.h
@@ -24,19 +24,6 @@
 #include <caml/alloc.h>
 #include <caml/mlvalues.h>
 
-/* Replacement if caml_alloc_initialized_string is missing, added
- * to OCaml runtime in 2017.
- */
-#ifndef HAVE_CAML_ALLOC_INITIALIZED_STRING
-static inline value
-caml_alloc_initialized_string (mlsize_t len, const char *p)
-{
-  value sv = caml_alloc_string (len);
-  memcpy ((char *) String_val (sv), p, len);
-  return sv;
-}
-#endif
-
 #define Guestfs_val(v) (*((guestfs_h **)Data_custom_val(v)))
 extern void guestfs_int_ocaml_raise_error (guestfs_h *g, const char *func)
   Noreturn;