diff --git a/arch/alpha/include/asm/pgtable.h b/arch/alpha/include/asm/pgtable.h
index e9368c54be45..58870cad3351 100644
--- a/arch/alpha/include/asm/pgtable.h
+++ b/arch/alpha/include/asm/pgtable.h
@@ -126,6 +126,17 @@ struct vm_area_struct;
  */
 #define pgprot_noncached(prot)	(prot)
 
+/*
+ * All caching attribute macros are identity on Alpha, so the generic
+ * pgprot_modify() degenerates to tautological self-comparisons.
+ * Override it to just return newprot directly.
+ */
+#define pgprot_modify pgprot_modify
+static inline pgprot_t pgprot_modify(pgprot_t oldprot, pgprot_t newprot)
+{
+	return newprot;
+}
+
 /*
  * ZERO_PAGE is a global shared page that is always zero:  used
  * for zero-mapped memory areas etc..