diff --git a/ext/speex/meson.build b/ext/speex/meson.build
index b682f08..c87ef6a 100644
--- a/ext/speex/meson.build
+++ b/ext/speex/meson.build
@@ -5,11 +5,15 @@
 ]
 
 speex_dep = dependency('speex', version : '>=1.1.6', required : false)
+windows_args = []
+if host_system == 'windows'
+  windows_args = ['-DWIN32']
+endif
 
 if speex_dep.found()
   gstspeex = library('gstspeex',
     speex_sources,
-    c_args : gst_plugins_good_args + ['-DGST_USE_UNSTABLE_API'],
+    c_args : gst_plugins_good_args + ['-DGST_USE_UNSTABLE_API'] + windows_args,
     link_args : noseh_link_args,
     include_directories : [configinc],
     dependencies : [gstbase_dep, gsttag_dep, gstaudio_dep, speex_dep, libm],