diff --git a/ruby.c b/ruby.c
index 55d5bf090c..b5c705002a 100644
--- a/ruby.c
+++ b/ruby.c
@@ -1041,6 +1041,10 @@ setup_ujit_options(const char *s, struct rb_ujit_options *ujit_opt)
     if (opt_match_noarg(s, l, "stats")) {
         ujit_opt->gen_stats = true;
     }
+    else {
+        rb_raise(rb_eRuntimeError,
+                 "invalid ujit option `%s' (--help will show valid ujit options)", s);
+    }
 }
 
 #if USE_MJIT
diff --git a/ujit_codegen.c b/ujit_codegen.c
index 010e98ae86..bb0b802fc4 100644
--- a/ujit_codegen.c
+++ b/ujit_codegen.c
@@ -180,6 +180,7 @@ ujit_gen_block(ctx_t* ctx, block_t* block)
         }
 
 #if RUBY_DEBUG
+        // Count instructions executed by the JIT
         mov(cb, REG0, const_ptr_opnd((void *)&rb_ujit_exec_insns_count));
         add(cb, mem_opnd(64, REG0, 0), imm_opnd(1));
 #endif