diff --git a/lib/base64.c b/lib/base64.c
index 325c7332b049..e46be3a55585 100644
--- a/lib/base64.c
+++ b/lib/base64.c
@@ -52,11 +52,14 @@ static const char base64_tables[][65] = {
 	INIT_32(0x60, ch_62, ch_63), \
 	[0x80 ... 0xff] = -1 }
 
+__diag_push();
+__diag_ignore(clang, all, "-Wconstant-conversion", "https://github.com/llvm/llvm-project/issues/223923");
 static const s8 base64_rev_maps[][256] = {
 	[BASE64_STD] = BASE64_REV_INIT('+', '/'),
 	[BASE64_URLSAFE] = BASE64_REV_INIT('-', '_'),
 	[BASE64_IMAP] = BASE64_REV_INIT('+', ',')
 };
+__diag_pop();
 
 #undef BASE64_REV_INIT
 #undef INIT_32