diff --git a/include/os.h b/include/os.h
index 947c6a0c3..7823b795d 100644
--- a/include/os.h
+++ b/include/os.h
@@ -54,7 +54,7 @@ SOFTWARE.
 #include "misc.h"
 #define ALLOCATE_LOCAL_FALLBACK(_size) Xalloc((unsigned long)(_size))
 #define DEALLOCATE_LOCAL_FALLBACK(_ptr) Xfree((pointer)(_ptr))
-#include "Xalloca.h"
+#include <X11/Xalloca.h>
 #ifndef IN_MODULE
 #include <stdarg.h>
 #else