diff --git a/arch/riscv/mmu.cpp b/arch/riscv/mmu.cpp
index 585ada6b..3804f6fa 100644
--- a/arch/riscv/mmu.cpp
+++ b/arch/riscv/mmu.cpp
@@ -113,7 +113,7 @@ void riscv_set_satp(uint asid, paddr_t pt) {
 #endif
 
     // make sure the asid is in range
-    DEBUG_ASSERT_MSG((asid & riscv_asid_mask) == asid, "asid %#x mask %#x\n", asid, riscv_asid_mask);
+    DEBUG_ASSERT_MSG((asid & riscv_asid_mask) == asid, "asid %#x mask %#lx\n", asid, riscv_asid_mask);
     satp |= (ulong)asid << RISCV_SATP_ASID_SHIFT;
 
     // make sure the page table is aligned
diff --git a/lib/libc/include/assert.h b/lib/libc/include/assert.h
index ad73058a..7b476fe6 100644
--- a/lib/libc/include/assert.h
+++ b/lib/libc/include/assert.h
@@ -88,6 +88,6 @@ __BEGIN_CDECLS
 // The following functions are called when an assert fails.
 void assert_fail(const char *file, int line, const char *expression) __NO_RETURN __NO_INLINE;
 void assert_fail_msg(const char *file, int line, const char *expression, const char *fmt,
-                     ...) __NO_RETURN __NO_INLINE;
+                     ...) __PRINTFLIKE(4, 5) __NO_RETURN __NO_INLINE;
 
 __END_CDECLS