diff --git a/eval.c b/eval.c
index 2596921..7852cf5 100644
--- a/eval.c
+++ b/eval.c
@@ -604,8 +604,7 @@ rb_block_given_p(void)
 {
     rb_thread_t *th = GET_THREAD();
 
-    if ((th->cfp->lfp[0] & 0x02) == 0 &&
-	GC_GUARDED_PTR_REF(th->cfp->lfp[0])) {
+    if (!IN_CLASS_DEF(th->cfp) && BLOCK_PTR_REF(th->cfp)) {
 	return TRUE;
     }
     else {
@@ -980,12 +979,12 @@ errinfo_place(rb_thread_t *th)
     while (RUBY_VM_VALID_CONTROL_FRAME_P(cfp, end_cfp)) {
 	if (RUBY_VM_NORMAL_ISEQ_P(cfp->iseq)) {
 	    if (cfp->iseq->type == ISEQ_TYPE_RESCUE) {
-		return &cfp->dfp[-2];
+		return &ERRINFO(cfp);
 	    }
 	    else if (cfp->iseq->type == ISEQ_TYPE_ENSURE &&
-		     TYPE(cfp->dfp[-2]) != T_NODE &&
-		     !FIXNUM_P(cfp->dfp[-2])) {
-		return &cfp->dfp[-2];
+		     TYPE(ERRINFO(cfp)) != T_NODE &&
+		     !FIXNUM_P(ERRINFO(cfp))) {
+		return &ERRINFO(cfp);
 	    }
 	}
 	cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
diff --git a/eval_intern.h b/eval_intern.h
index 549953a..de1a2dc 100644
--- a/eval_intern.h
+++ b/eval_intern.h
@@ -5,7 +5,7 @@
 #include "vm_core.h"
 
 #define PASS_PASSED_BLOCK_TH(th) do { \
-    (th)->passed_block = GC_GUARDED_PTR_REF((rb_block_t *)(th)->cfp->lfp[0]); \
+    (th)->passed_block = BLOCK_PTR_REF((th)->cfp); \
     (th)->cfp->flag |= VM_FRAME_FLAG_PASSED; \
 } while (0)
 
diff --git a/proc.c b/proc.c
index 0489dd9..78152c4 100644
--- a/proc.c
+++ b/proc.c
@@ -384,16 +384,16 @@ proc_new(VALUE klass, int is_lambda)
     rb_control_frame_t *cfp = th->cfp;
     rb_block_t *block;
 
-    if ((GC_GUARDED_PTR_REF(cfp->lfp[0])) != 0) {
+    if (BLOCK_PTR_REF(cfp) != 0) {
 
-	block = GC_GUARDED_PTR_REF(cfp->lfp[0]);
+	block = BLOCK_PTR_REF(cfp);
     }
     else {
 	cfp = RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp);
 
-	if ((GC_GUARDED_PTR_REF(cfp->lfp[0])) != 0) {
+	if (BLOCK_PTR_REF(cfp) != 0) {
 
-	    block = GC_GUARDED_PTR_REF(cfp->lfp[0]);
+	    block = BLOCK_PTR_REF(cfp);
 
 	    if (is_lambda) {
 		rb_warn("tried to create Proc object without a block");
diff --git a/vm.c b/vm.c
index e62c9a4..bed2684 100644
--- a/vm.c
+++ b/vm.c
@@ -69,7 +69,7 @@ static inline VALUE
 rb_vm_set_finish_env(rb_thread_t * th)
 {
     vm_push_frame(th, 0, VM_FRAME_MAGIC_FINISH,
-		  Qnil, th->cfp->lfp[0], 0,
+		  Qnil, BLOCK_PTR_RAW(th->cfp), 0,
 		  th->cfp->sp, 0, 1);
     th->cfp->pc = (VALUE *)&finish_insn_seq[0];
     return Qtrue;
@@ -109,7 +109,7 @@ vm_set_eval_stack(rb_thread_t * th, VALUE iseqval, const NODE *cref)
 		  th->cfp->sp, block->lfp, iseq->local_size);
 
     if (cref) {
-	th->cfp->dfp[-1] = (VALUE)cref;
+	CREF(th->cfp) = (VALUE)cref;
     }
 
     CHECK_STACK_OVERFLOW(th->cfp, iseq->stack_max);
@@ -476,7 +476,7 @@ rb_vm_make_proc(rb_thread_t *th, const rb_block_t *block, VALUE klass)
 	rb_bug("rb_vm_make_proc: Proc value is already created.");
     }
 
-    if (GC_GUARDED_PTR_REF(cfp->lfp[0])) {
+    if (BLOCK_PTR_REF(cfp)) {
 	    rb_proc_t *p;
 
 	    blockprocval = vm_make_proc_from_block(
@@ -551,7 +551,7 @@ invoke_block_from_c(rb_thread_t *th, const rb_block_t *block,
 	th->passed_me = 0;
 
 	if (cref) {
-	    th->cfp->dfp[-1] = (VALUE)cref;
+	    CREF(th->cfp) = (VALUE)cref;
 	}
 
 	return vm_exec(th);
@@ -564,7 +564,7 @@ invoke_block_from_c(rb_thread_t *th, const rb_block_t *block,
 static inline const rb_block_t *
 check_block(rb_thread_t *th)
 {
-    const rb_block_t *blockptr = GC_GUARDED_PTR_REF(th->cfp->lfp[0]);
+    const rb_block_t *blockptr = BLOCK_PTR_REF(th->cfp);
 
     if (blockptr == 0) {
 	rb_vm_localjump_error("no block given", Qnil, 0);
diff --git a/vm_core.h b/vm_core.h
index dea19fa..0dbe0f5 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -707,4 +707,12 @@ int rb_thread_check_trap_pending(void);
 #pragma GCC visibility pop
 #endif
 
+#define BLOCK_PTR_RAW(cfp) (cfp)->lfp[0]
+#define BLOCK_PTR_REF(cfp) (GC_GUARDED_PTR_REF(BLOCK_PTR_RAW(cfp)))
+#define IN_CLASS_DEF(cfp) (BLOCK_PTR_RAW(cfp) & 0x02)
+#define SET_BLOCK_PTR(cfp, ptr) BLOCK_PTR_RAW(cfp) = GC_GUARDED_PTR(ptr)
+#define ERRINFO(cfp) (cfp)->dfp[-2]
+#define CREF(cfp) (cfp)->dfp[-1]
+#define PREV_DFP_REF(cfp) GC_GUARDED_PTR_REF((cfp)->dfp[0])
+
 #endif /* RUBY_VM_CORE_H */
diff --git a/vm_eval.c b/vm_eval.c
index 122837b..02f9955 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -845,7 +845,7 @@ rb_iterate(VALUE (* it_proc) (VALUE), VALUE data1,
 		blockptr->proc = 0;
 	    }
 	    else {
-		blockptr = GC_GUARDED_PTR_REF(th->cfp->lfp[0]);
+		blockptr = BLOCK_PTR_REF(th->cfp);
 	    }
 	    th->passed_block = blockptr;
 	}
@@ -1195,10 +1195,10 @@ yield_under(VALUE under, VALUE self, VALUE values)
     rb_block_t block, *blockptr;
     NODE *cref;
 
-    if ((blockptr = GC_GUARDED_PTR_REF(th->cfp->lfp[0])) != 0) {
+    if ((blockptr = BLOCK_PTR_REF(th->cfp)) != 0) {
 	block = *blockptr;
 	block.self = self;
-	th->cfp->lfp[0] = GC_GUARDED_PTR(&block);
+	SET_BLOCK_PTR(th->cfp, &block);
     }
     cref = vm_cref_push(th, under, NOEX_PUBLIC, blockptr);
     cref->flags |= NODE_FL_CREF_PUSHED_BY_EVAL;
@@ -1673,7 +1673,7 @@ rb_f_local_variables(void)
 	}
 	if (cfp->lfp != cfp->dfp) {
 	    /* block */
-	    VALUE *dfp = GC_GUARDED_PTR_REF(cfp->dfp[0]);
+	    VALUE *dfp = PREV_DFP_REF(cfp);
 
 	    if (vm_collect_local_variables_in_heap(th, dfp, ary)) {
 		break;
@@ -1721,8 +1721,8 @@ rb_f_block_given_p(void)
     cfp = vm_get_ruby_level_caller_cfp(th, RUBY_VM_PREVIOUS_CONTROL_FRAME(cfp));
 
     if (cfp != 0 &&
-	(cfp->lfp[0] & 0x02) == 0 &&
-	GC_GUARDED_PTR_REF(cfp->lfp[0])) {
+	!IN_CLASS_DEF(cfp) &&
+	BLOCK_PTR_REF(cfp)) {
 	return Qtrue;
     }
     else {