diff --git a/Makefile b/Makefile
index cd84720..a08420d 100644
--- a/Makefile
+++ b/Makefile
@@ -15,8 +15,8 @@ PACKS = camlpdf
 
 CFLAGS = -fPIC
 OCAMLFLAGS = -bin-annot
-OCAMLNCFLAGS = -g -safe-string -w -3
-OCAMLBCFLAGS = -g -safe-string -w -3
+OCAMLNCFLAGS = -g -safe-string
+OCAMLBCFLAGS = -g -safe-string
 OCAMLLDFLAGS = -g
 
 all : native-code native-code-library byte-code-library top htdoc
diff --git a/cpdfcommand.ml b/cpdfcommand.ml
index 3b68812..9cb244e 100644
--- a/cpdfcommand.ml
+++ b/cpdfcommand.ml
@@ -1113,7 +1113,7 @@ let setaddtext s =
   setop (AddText s) ()
 
 let parse_color s =
-  match String.lowercase s with
+  match String.lowercase_ascii s with
   | "white" -> Cpdfaddtext.RGB (1., 1., 1.)
   | "black" -> Cpdfaddtext.RGB (0., 0., 0.)
   | "red" -> Cpdfaddtext.RGB (1., 0., 0.)
diff --git a/cpdfimage.ml b/cpdfimage.ml
index cc85b29..97ddb40 100644
--- a/cpdfimage.ml
+++ b/cpdfimage.ml
@@ -5,7 +5,7 @@ open Pdfio
 let pnm_to_channel_24 channel w h s =
   let white () = output_char channel ' ' 
   and newline () = output_char channel '\n'
-  and output_string = Pervasives.output_string channel in
+  and output_string = Stdlib.output_string channel in
     output_string "P6";
     white ();
     output_string (string_of_int w);
diff --git a/cpdfxmlm.ml b/cpdfxmlm.ml
index 3430e91..5f94f5a 100644
--- a/cpdfxmlm.ml
+++ b/cpdfxmlm.ml
@@ -1125,7 +1125,7 @@ module String = struct
   let empty = ""
   let length = String.length
   let append = ( ^ )
-  let lowercase = String.lowercase
+  let lowercase = String.lowercase_ascii
   let iter f s =
     let len = Std_string.length s in
     let pos = ref ~-1 in