--- a/src/egl/formats.c
+++ b/src/egl/formats.c
@@ -1,6 +1,11 @@
 #include <wlm/egl/formats.h>
 #include <GLES2/gl2ext.h>
 
+/* Slackware 15.0 (mesa 21.3) gl2ext.h lacks GL_EXT_texture_format_BGR888 */
+#ifndef GL_BGR_EXT
+#define GL_BGR_EXT 0x80E0
+#endif
+
 // TODO: add missing wl_shm, drm, and spa formats
 // TODO: verify these format assignments are correct
 // TODO: check gl formats