diff --git a/include/mruby/ops.h b/include/mruby/ops.h
index 9e4432f4d..51b8a4da0 100644
--- a/include/mruby/ops.h
+++ b/include/mruby/ops.h
@@ -113,6 +113,8 @@ OPCODE(CLASS,      BB)       /* R[a] = newclass(R[a],Syms[b],R[a+1]) */
 OPCODE(MODULE,     BB)       /* R[a] = newmodule(R[a],Syms[b]) */
 OPCODE(EXEC,       BB)       /* R[a] = blockexec(R[a],Irep[b]) */
 OPCODE(DEF,        BB)       /* R[a].newmethod(Syms[b],R[a+1]); R[a] = Syms[b] */
+OPCODE(TDEF,       BBB)      /* target_class.newmethod(Syms[b],Irep[c]); R[a] = Syms[b] */
+OPCODE(SDEF,       BBB)      /* R[a].singleton_class.newmethod(Syms[b],Irep[c]); R[a] = Syms[b] */
 OPCODE(ALIAS,      BB)       /* alias_method(target_class,Syms[a],Syms[b]) */
 OPCODE(UNDEF,      B)        /* undef_method(target_class,Syms[a]) */
 OPCODE(SCLASS,     B)        /* R[a] = R[a].singleton_class */
diff --git a/mrbgems/mruby-compiler/core/codegen.c b/mrbgems/mruby-compiler/core/codegen.c
index e0da700e5..080380839 100644
--- a/mrbgems/mruby-compiler/core/codegen.c
+++ b/mrbgems/mruby-compiler/core/codegen.c
@@ -5017,12 +5017,18 @@ codegen_def(codegen_scope *s, node *varnode, int val)
   /* For NODE_DEF, args should contain the full locals structure from defn_setup */
   int idx = lambda_body(s, def_n->locals, def_n->args, def_n->body, 0);
 
-  genop_1(s, OP_TCLASS, cursp());
-  push();
-  genop_2(s, OP_METHOD, cursp(), idx);
-  push(); pop();
-  pop();
-  genop_2(s, OP_DEF, cursp(), sym);
+  if (idx <= 0xff) {
+    /* TDEF fusion: TCLASS + METHOD + DEF -> TDEF */
+    genop_3(s, OP_TDEF, cursp(), sym, idx);
+  }
+  else {
+    genop_1(s, OP_TCLASS, cursp());
+    push();
+    genop_2(s, OP_METHOD, cursp(), idx);
+    push(); pop();
+    pop();
+    genop_2(s, OP_DEF, cursp(), sym);
+  }
   if (val) push();
 }
 
@@ -6400,12 +6406,18 @@ codegen_sdef(codegen_scope *s, const node *varnode, int val)
 
   codegen(s, recv, VAL);
   pop();
-  genop_1(s, OP_SCLASS, cursp());
-  push();
-  genop_2(s, OP_METHOD, cursp(), idx);
-  push(); pop();
-  pop();
-  genop_2(s, OP_DEF, cursp(), sym);
+  if (idx <= 0xff) {
+    /* SDEF fusion: SCLASS + METHOD + DEF -> SDEF */
+    genop_3(s, OP_SDEF, cursp(), sym, idx);
+  }
+  else {
+    genop_1(s, OP_SCLASS, cursp());
+    push();
+    genop_2(s, OP_METHOD, cursp(), idx);
+    push(); pop();
+    pop();
+    genop_2(s, OP_DEF, cursp(), sym);
+  }
   if (val) push();
 }
 
diff --git a/src/codedump.c b/src/codedump.c
index 14191c0f3..308dee72f 100644
--- a/src/codedump.c
+++ b/src/codedump.c
@@ -427,6 +427,12 @@ codedump(mrb_state *mrb, const mrb_irep *irep, FILE *out)
     CASE(OP_DEF, BB):
       fprintf(out, "DEF\t\tR%d\t:%s\t(R%d)\n", a, mrb_sym_dump(mrb, irep->syms[b]),a+1);
       break;
+    CASE(OP_TDEF, BBB):
+      fprintf(out, "TDEF\t\tR%d\t:%s\tI[%d]\n", a, mrb_sym_dump(mrb, irep->syms[b]), c);
+      break;
+    CASE(OP_SDEF, BBB):
+      fprintf(out, "SDEF\t\tR%d\t:%s\tI[%d]\n", a, mrb_sym_dump(mrb, irep->syms[b]), c);
+      break;
     CASE(OP_UNDEF, B):
       fprintf(out, "UNDEF\t\t:%s\n", mrb_sym_dump(mrb, irep->syms[a]));
       break;
diff --git a/src/vm.c b/src/vm.c
index 667d09cf1..3f99147ba 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -3396,6 +3396,42 @@ RETRY_TRY_BLOCK:
       NEXT;
     }
 
+    CASE(OP_TDEF, BBB) {
+      struct RClass *target = check_target_class(mrb);
+      if (!target) goto L_RAISE;
+      struct RProc *p = mrb_proc_new(mrb, irep->reps[c]);
+      mrb_method_t m;
+      mrb_sym mid = irep->syms[b];
+
+      p->flags |= MRB_PROC_SCOPE | MRB_PROC_STRICT;
+      MRB_METHOD_FROM_PROC(m, p);
+      MRB_METHOD_SET_VISIBILITY(m, MRB_METHOD_VDEFAULT_FL);
+      mrb_define_method_raw(mrb, target, mid, m);
+      mrb_method_added(mrb, target, mid);
+      ci = mrb->c->ci;
+      mrb_gc_arena_restore(mrb, ai);
+      regs[a] = mrb_symbol_value(mid);
+      NEXT;
+    }
+
+    CASE(OP_SDEF, BBB) {
+      mrb_value recv = regs[a];
+      struct RClass *target = mrb_class_ptr(mrb_singleton_class(mrb, recv));
+      struct RProc *p = mrb_proc_new(mrb, irep->reps[c]);
+      mrb_method_t m;
+      mrb_sym mid = irep->syms[b];
+
+      p->flags |= MRB_PROC_SCOPE | MRB_PROC_STRICT;
+      MRB_METHOD_FROM_PROC(m, p);
+      MRB_METHOD_SET_VISIBILITY(m, MRB_METHOD_VDEFAULT_FL);
+      mrb_define_method_raw(mrb, target, mid, m);
+      mrb_method_added(mrb, target, mid);
+      ci = mrb->c->ci;
+      mrb_gc_arena_restore(mrb, ai);
+      regs[a] = mrb_symbol_value(mid);
+      NEXT;
+    }
+
     CASE(OP_SCLASS, B) {
       regs[a] = mrb_singleton_class(mrb, regs[a]);
       mrb_gc_arena_restore(mrb, ai);