diff --git a/src/typepair.h b/src/typepair.h
index f67494cf63..cc1c72424b 100644
--- a/src/typepair.h
+++ b/src/typepair.h
@@ -19,6 +19,12 @@
 #ifndef SRC_TYPEPAIR_H_
 #define SRC_TYPEPAIR_H_
 
+// X11 likes to #define Bool leading to confusing error messages.
+// If its defined, undefine it.
+#ifdef Bool
+#undef Bool
+#endif
+
 namespace tint {
 
 namespace ast {