diff --git a/yjit/src/asm/mod.rs b/yjit/src/asm/mod.rs
index 2bd776ec812a4e..524d6341f590ce 100644
--- a/yjit/src/asm/mod.rs
+++ b/yjit/src/asm/mod.rs
@@ -136,6 +136,10 @@ impl CodeBlock {
         };
         cb.page_end_reserve = cb.jmp_ptr_bytes();
         cb.write_pos = cb.page_start();
+
+        #[cfg(not(test))]
+        assert_eq!(0, mem_size % page_size, "partially in-bounds code pages should be impossible");
+
         cb
     }