diff --git a/tools/ci/amd64/clang/msan.supp b/tools/ci/amd64/clang/msan.supp
index e679c25..88f01b7 100644
--- a/tools/ci/amd64/clang/msan.supp
+++ b/tools/ci/amd64/clang/msan.supp
@@ -69,3 +69,18 @@ fun:Fixture::create_component*
 
 fun:_XData32
 src:read_iovec
+
+# Ignore system X11/XCB libraries (not MSan-instrumented)
+fun:_XData32
+fun:XChangeProperty
+fun:_XSend
+fun:_XFlush
+fun:XFlush
+fun:write_vec
+fun:_xcb_conn_wait
+fun:_xcb_out_send
+fun:xcb_writev
+
+# Alternatively, blanket-ignore the libraries themselves
+src:/msan/lib/libX11.so.*
+src:/msan/lib/libxcb.so.*