diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4fdacec..95f0d06 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,11 @@
 
 ## master
 
+## Version 2.1.4 (2021-10-27)
+
+* add support for `format_string`, so buffer and target savers are better at
+  writing the correct format [jcupitt]
+
 ## Version 2.1.3 (2021-8-23)
 
 * fix a gtype size error on win64 [danini-the-panini]
diff --git a/VERSION b/VERSION
index ac2cdeb..7d2ed7c 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.1.3
+2.1.4
diff --git a/lib/vips/image.rb b/lib/vips/image.rb
index 1b800d1..6bc948b 100644
--- a/lib/vips/image.rb
+++ b/lib/vips/image.rb
@@ -626,7 +626,12 @@ def write_to_buffer format_string, **opts
       saver = Vips.vips_foreign_find_save_buffer filename
       raise Vips::Error if saver.nil?
 
-      buffer = Vips::Operation.call saver, [self], opts, option_string
+      # note the format_string for savers
+      image = self.mutate do |x|
+        x.set_type! Vips::REFSTR_TYPE, "format-string", format_string
+      end
+
+      buffer = Vips::Operation.call saver, [image], opts, option_string
       raise Vips::Error if buffer.nil?
 
       write_gc
@@ -667,7 +672,12 @@ def write_to_target target, format_string, **opts
       saver = Vips.vips_foreign_find_save_target filename
       raise Vips::Error if saver.nil?
 
-      Vips::Operation.call saver, [self, target], opts, option_string
+      # note the format_string for savers
+      image = self.mutate do |x|
+        x.set_type! Vips::REFSTR_TYPE, "format-string", format_string
+      end
+
+      Vips::Operation.call saver, [image, target], opts, option_string
       write_gc
     end
 
diff --git a/lib/vips/version.rb b/lib/vips/version.rb
index efc5ffb..d1f9890 100644
--- a/lib/vips/version.rb
+++ b/lib/vips/version.rb
@@ -1,3 +1,3 @@
 module Vips
-  VERSION = "2.1.3"
+  VERSION = "2.1.4"
 end