diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index e821fd533..85d1af61f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -163,6 +163,9 @@ Any user-visible change should have a Changelog entry:
 - with the issue number `PR#{N}` if from mantis, `GPR#{N}` if from github
   (several numbers separated by commas can be used)
 
+- maintaining the order: each section lists Mantis PRs first in ascending
+  numerical order, followed by Github PRs
+
 - with a concise readable description of the change (possibly taken
   from a commit message, but it should make sense to end-users
   reading release notes)
diff --git a/Changes b/Changes
index c76c2b7c5..d86fe1560 100644
--- a/Changes
+++ b/Changes
@@ -105,6 +105,8 @@ Runtime system:
   Shinwell, review by Damien Doligez)
 
 Standard library:
+- PR#6017, PR#7034, GPR#267: More efficient ifprintf implementation
+  (Jeremy Yallop, review by Gabriel Scherer)
 - PR#6316: Scanf.scanf failure on %u formats when reading big integers
   (Xavier Leroy, Benoît Vaugon)
 - PR#6390, GPR#36: expose Sys.{int_size,max_wosize} for improved js_of_ocaml
diff --git a/stdlib/camlinternalFormat.ml b/stdlib/camlinternalFormat.ml
index 22f555a6f..8d9f8d345 100644
--- a/stdlib/camlinternalFormat.ml
+++ b/stdlib/camlinternalFormat.ml
@@ -1709,7 +1709,6 @@ and make_float_padding_precision : type x y a b c d e f .
     fun w p x ->
       let str = fix_padding padty w (convert_float fconv p x) in
       make_printf k o (Acc_data_string (acc, str)) fmt
-
 and make_custom : type x y a b c d e f .
   (b -> (b, c) acc -> f) -> b -> (b, c) acc ->
   (a, b, c, d, e, f) fmt ->
@@ -1720,6 +1719,108 @@ and make_custom : type x y a b c d e f .
     fun x ->
       make_custom k o acc rest arity (f x)
 
+let const x _ = x
+
+let rec make_iprintf : type a b c d e f.
+  (b -> f) -> b -> (a, b, c, d, e, f) fmt -> a =
+  fun k o fmt -> match fmt with
+    | Char rest ->
+        const (make_iprintf k o rest)
+    | Caml_char rest ->
+        const (make_iprintf k o rest)
+    | String (No_padding, rest) ->
+        const (make_iprintf k o rest)
+    | String (Lit_padding _, rest) ->
+        const (make_iprintf k o rest)
+    | String (Arg_padding _, rest) ->
+        const (const (make_iprintf k o rest))
+    | Caml_string (No_padding, rest) ->
+        const (make_iprintf k o rest)
+    | Caml_string (Lit_padding _, rest) ->
+        const (make_iprintf k o rest)
+    | Caml_string (Arg_padding _, rest) ->
+        const (const (make_iprintf k o rest))
+    | Int (_, pad, prec, rest) ->
+        fn_of_padding_precision k o rest pad prec
+    | Int32 (_, pad, prec, rest) ->
+        fn_of_padding_precision k o rest pad prec
+    | Nativeint (_, pad, prec, rest) ->
+        fn_of_padding_precision k o rest pad prec
+    | Int64 (_, pad, prec, rest) ->
+        fn_of_padding_precision k o rest pad prec
+    | Float (_, pad, prec, rest) ->
+        fn_of_padding_precision k o rest pad prec
+    | Bool rest ->
+        const (make_iprintf k o rest)
+    | Alpha rest ->
+        const (const (make_iprintf k o rest))
+    | Theta rest ->
+        const (make_iprintf k o rest)
+    | Custom (arity, _, rest) ->
+        fn_of_custom_arity k o rest arity
+    | Reader _ ->
+        (* This case is impossible, by typing of formats.  See the
+           note in the corresponding case for make_printf. *)
+        assert false
+    | Flush rest ->
+        make_iprintf k o rest
+    | String_literal (_, rest) ->
+        make_iprintf k o rest
+    | Char_literal (_, rest) ->
+        make_iprintf k o rest
+    | Format_arg (_, _, rest) ->
+        const (make_iprintf k o rest)
+    | Format_subst (_, fmtty, rest) ->
+        fun (Format (fmt, _)) ->
+          make_iprintf k o
+            (concat_fmt (recast fmt fmtty) rest)
+    | Scan_char_set (_, _, rest) ->
+        const (make_iprintf k o rest)
+    | Scan_get_counter (_, rest) ->
+        const (make_iprintf k o rest)
+    | Scan_next_char rest ->
+        const (make_iprintf k o rest)
+    | Ignored_param (ign, rest) ->
+        make_ignored_param (fun x _ -> k x) o (End_of_acc) ign rest
+    | Formatting_lit (_, rest) ->
+        make_iprintf k o rest
+    | Formatting_gen (Open_tag (Format (fmt', _)), rest) ->
+        make_iprintf (fun koc -> make_iprintf k koc rest) o fmt'
+    | Formatting_gen (Open_box (Format (fmt', _)), rest) ->
+        make_iprintf (fun koc -> make_iprintf k koc rest) o fmt'
+    | End_of_format ->
+        k o
+and fn_of_padding_precision :
+  type x y z a b c d e f.
+  (b -> f) -> b -> (a, b, c, d, e, f) fmt ->
+  (x, y) padding -> (y, z -> a) precision -> x =
+  fun k o fmt pad prec -> match pad, prec with
+    | No_padding   , No_precision    ->
+        const (make_iprintf k o fmt)
+    | No_padding   , Lit_precision _ ->
+        const (make_iprintf k o fmt)
+    | No_padding   , Arg_precision   ->
+        const (const (make_iprintf k o fmt))
+    | Lit_padding _, No_precision    ->
+        const (make_iprintf k o fmt)
+    | Lit_padding _, Lit_precision _ ->
+        const (make_iprintf k o fmt)
+    | Lit_padding _, Arg_precision   ->
+        const (const (make_iprintf k o fmt))
+    | Arg_padding _, No_precision    ->
+        const (const (make_iprintf k o fmt))
+    | Arg_padding _, Lit_precision _ ->
+        const (const (make_iprintf k o fmt))
+    | Arg_padding _, Arg_precision   ->
+        const (const (const (make_iprintf k o fmt)))
+and fn_of_custom_arity : type x y a b c d e f .
+  (b -> f) -> b -> (a, b, c, d, e, f) fmt -> (a, x, y) custom_arity -> y =
+  fun k o fmt -> function
+    | Custom_zero ->
+        make_iprintf k o fmt
+    | Custom_succ arity ->
+        const (fn_of_custom_arity k o fmt arity)
+
 (******************************************************************************)
                           (* Continuations for make_printf *)
 
diff --git a/stdlib/camlinternalFormat.mli b/stdlib/camlinternalFormat.mli
index 036bcb0ec..2fb81f8bc 100644
--- a/stdlib/camlinternalFormat.mli
+++ b/stdlib/camlinternalFormat.mli
@@ -59,6 +59,8 @@ val make_printf :
   ('b -> ('b, 'c) acc -> 'd) -> 'b -> ('b, 'c) acc ->
   ('a, 'b, 'c, 'c, 'c, 'd) CamlinternalFormatBasics.fmt -> 'a
 
+val make_iprintf : ('b -> 'f) -> 'b -> ('a, 'b, 'c, 'd, 'e, 'f) fmt -> 'a
+
 val output_acc : out_channel -> (out_channel, unit) acc -> unit
 val bufput_acc : Buffer.t -> (Buffer.t, unit) acc -> unit
 val strput_acc : Buffer.t -> (unit, string) acc -> unit
diff --git a/stdlib/format.ml b/stdlib/format.ml
index 3ab79e254..194d3fcd3 100644
--- a/stdlib/format.ml
+++ b/stdlib/format.ml
@@ -1181,10 +1181,7 @@ let kfprintf k ppf (Format (fmt, _)) =
     ppf End_of_acc fmt
 
 and ikfprintf k ppf (Format (fmt, _)) =
-  make_printf
-    (fun _ _ -> k ppf)
-    ppf End_of_acc fmt
-;;
+  make_iprintf k ppf fmt
 
 let fprintf ppf = kfprintf ignore ppf;;
 let ifprintf ppf = ikfprintf ignore ppf;;
diff --git a/stdlib/printf.ml b/stdlib/printf.ml
index 1152429f9..e6f264074 100644
--- a/stdlib/printf.ml
+++ b/stdlib/printf.ml
@@ -19,7 +19,7 @@ let kfprintf k o (Format (fmt, _)) =
 let kbprintf k b (Format (fmt, _)) =
   make_printf (fun b acc -> bufput_acc b acc; k b) b End_of_acc fmt
 let ikfprintf k oc (Format (fmt, _)) =
-  make_printf (fun oc _ -> k oc) oc End_of_acc fmt
+  make_iprintf k oc fmt
 
 let fprintf oc fmt = kfprintf ignore oc fmt
 let bprintf b fmt = kbprintf ignore b fmt