diff --git a/src/core/jbuild b/src/core/jbuild
index c93cbc7e..172c8daf 100644
--- a/src/core/jbuild
+++ b/src/core/jbuild
@@ -3,8 +3,7 @@
   ((name containers)
    (public_name containers)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always -nolabels -open CCMonomorphic))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -nolabels -open CCMonomorphic))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (bytes result containers.monomorphic))
   ))
diff --git a/src/data/jbuild b/src/data/jbuild
index 80ac4bce..9fcf9861 100644
--- a/src/data/jbuild
+++ b/src/data/jbuild
@@ -3,8 +3,7 @@
   ((name containers_data)
    (public_name containers.data)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (bytes result))
   ))
diff --git a/src/iter/jbuild b/src/iter/jbuild
index 60ca4553..bade997f 100644
--- a/src/iter/jbuild
+++ b/src/iter/jbuild
@@ -3,8 +3,7 @@
   ((name containers_iter)
    (public_name containers.iter)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (bytes result))
   ))
diff --git a/src/jbuild b/src/jbuild
new file mode 100644
index 00000000..8373c9ad
--- /dev/null
+++ b/src/jbuild
@@ -0,0 +1,10 @@
+
+
+(rule
+  ((targets (flambda.flags))
+   (deps ((file mkflags.ml)))
+   (fallback)
+   (action
+     (run ocaml ./mkflags.ml))
+  ))
+
diff --git a/src/mkflags.ml b/src/mkflags.ml
new file mode 100644
index 00000000..591df576
--- /dev/null
+++ b/src/mkflags.ml
@@ -0,0 +1,13 @@
+ let () =
+   let major, minor =
+     Scanf.sscanf Sys.ocaml_version "%u.%u"
+       (fun major minor -> major, minor)
+   in
+   let after_4_3 = (major, minor) >= (4, 3) in
+   let flags_file = open_out "flambda.flags" in
+   if after_4_3 then (
+     output_string flags_file "(-O3 -unbox-closures -unbox-closures-factor 20 -color always)\n";
+   ) else (
+     output_string flags_file "()\n";
+   );
+   close_out flags_file
diff --git a/src/monomorphic/jbuild b/src/monomorphic/jbuild
index 0944bf5f..4eeaac49 100644
--- a/src/monomorphic/jbuild
+++ b/src/monomorphic/jbuild
@@ -3,8 +3,7 @@
   ((name containers_monomorphic)
    (public_name containers.monomorphic)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries ())
   ))
diff --git a/src/sexp/jbuild b/src/sexp/jbuild
index cc7f71c0..b3c35302 100644
--- a/src/sexp/jbuild
+++ b/src/sexp/jbuild
@@ -3,9 +3,8 @@
   ((name containers_sexp)
    (public_name containers.sexp)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (bytes result))
   ))
 
diff --git a/src/threads/jbuild b/src/threads/jbuild
index c698afac..7af8cbef 100644
--- a/src/threads/jbuild
+++ b/src/threads/jbuild
@@ -4,9 +4,8 @@
    (public_name containers.thread)
    (wrapped false)
    (optional)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (containers threads))
   ))
 
diff --git a/src/top/jbuild b/src/top/jbuild
index d42f7276..3bd8a254 100644
--- a/src/top/jbuild
+++ b/src/top/jbuild
@@ -4,9 +4,8 @@
   ((name containers_top)
    (public_name containers.top)
    (wrapped false)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (compiler-libs.common containers containers.data
                containers.unix containers.sexp containers.iter))
   ))
diff --git a/src/unix/.merlin b/src/unix/.merlin
index 9b310e15..d86c675f 100644
--- a/src/unix/.merlin
+++ b/src/unix/.merlin
@@ -1,5 +1,5 @@
 B ../../_build/default/src/unix
-FLG -w -40 -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always
+FLG -w -40 -w +a-4-42-44-48-50-58-32-60@8 -safe-string
 PKG bytes
 PKG result
 PKG unix
diff --git a/src/unix/jbuild b/src/unix/jbuild
index c46a4c25..6502a9d3 100644
--- a/src/unix/jbuild
+++ b/src/unix/jbuild
@@ -4,8 +4,7 @@
    (public_name containers.unix)
    (wrapped false)
    (optional)
-   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string -color always))
-   (ocamlopt_flags (:standard -O3 -color always
-                    -unbox-closures -unbox-closures-factor 20))
+   (flags (:standard -w +a-4-42-44-48-50-58-32-60@8 -safe-string))
+   (ocamlopt_flags (:standard (:include ../flambda.flags)))
    (libraries (bytes result unix))
   ))