diff --git a/meson.build b/meson.build
index 24d239f3..d03cb67c 100644
--- a/meson.build
+++ b/meson.build
@@ -3,7 +3,9 @@ project('vips', 'c', 'cpp',
     meson_version: '>=0.56',
     default_options: [
         # this is what glib uses (one of our required deps), so we use it too
-        'c_std=gnu99'
+        'c_std=gnu99',
+        # turn off asserts etc. in release mode
+        'b_ndebug=if-release'
     ]
 )
 
@@ -33,6 +35,21 @@ add_project_link_arguments(
     language: 'c',
 )
 
+# if we're optimising (eg. release mode) we turn off cast checks and
+# g_asserts
+if get_option('optimization') in ['2', '3', 's']
+    add_project_arguments('-DG_DISABLE_CAST_CHECKS', language : ['cpp', 'c'])
+    add_project_arguments('-DG_DISABLE_CHECKS', language : ['cpp', 'c'])
+    add_project_arguments('-DG_DISABLE_ASSERT', language : ['cpp', 'c'])
+endif
+
+# in debug mode we automatically enable leak checks and fatal warnings
+# also true for 'debugoptimized'
+if get_option('debug')
+    add_project_arguments('-DDEBUG_FATAL', language : ['cpp', 'c'])
+    add_project_arguments('-DDEBUG_LEAK', language : ['cpp', 'c'])
+endif
+
 cc = meson.get_compiler('c')
 cpp = meson.get_compiler('cpp')