diff --git a/include/ruby/assert.h b/include/ruby/assert.h
index 7e59da6662c90a..ac9b9c8cc35239 100644
--- a/include/ruby/assert.h
+++ b/include/ruby/assert.h
@@ -62,8 +62,8 @@ RBIMPL_SYMBOL_EXPORT_END()
 # define RBIMPL_ASSERT_FUNC RBIMPL_CAST((const char *)0)
 #endif
 
-#define RUBY_ASSERT_FAIL(expr) \
-    rb_assert_failure(__FILE__, __LINE__, RBIMPL_ASSERT_FUNC, #expr)
+#define RUBY_ASSERT_FAIL(mesg) \
+    rb_assert_failure(__FILE__, __LINE__, RBIMPL_ASSERT_FUNC, mesg)
 
 #define RUBY_ASSERT_MESG(expr, mesg) \
     (RB_LIKELY(expr) ? RBIMPL_ASSERT_NOTHING : RUBY_ASSERT_FAIL(mesg))
diff --git a/include/ruby/internal/globals.h b/include/ruby/internal/globals.h
index 82695916906879..e0bef2db24daa5 100644
--- a/include/ruby/internal/globals.h
+++ b/include/ruby/internal/globals.h
@@ -148,7 +148,7 @@ rb_class_of(VALUE obj)
 #if RUBY_NDEBUG
     RBIMPL_UNREACHABLE_RETURN(Qfalse);
 #else
-    RUBY_ASSERT_FAIL(rb_class_of);
+    RUBY_ASSERT_FAIL("unexpected type");
 #endif
 }