Index: src/oo.c
===================================================================
--- src/oo.c	(revision 41448)
+++ src/oo.c	(revision 41449)
@@ -743,7 +743,7 @@
         for (entry = 0; entry < TBL_SIZE; ++entry) {
             Meth_cache_entry *e = mc->idx[type][entry];
             while (e) {
-                Parrot_gc_mark_PObj_alive(interp, (PObj *)e->pmc);
+                Parrot_gc_mark_PMC_alive(interp, e->pmc);
                 e = e->next;
             }
         }
Index: src/pmc/capture.pmc
===================================================================
--- src/pmc/capture.pmc	(revision 41448)
+++ src/pmc/capture.pmc	(revision 41449)
@@ -507,8 +507,7 @@
             return;
 
         for (i = PARROT_CAPTURE(SELF)->data_size - 1; i >= 0; --i)
-            if (data[i])
-                Parrot_gc_mark_PObj_alive(interp, (PObj *)data[i]);
+            Parrot_gc_mark_PMC_alive(interp, data[i]);
     }
 
 /*
Index: src/pmc/context.pmc
===================================================================
--- src/pmc/context.pmc	(revision 41448)
+++ src/pmc/context.pmc	(revision 41449)
@@ -60,42 +60,16 @@
         if (!ctx)
             return;
 
-        obj = (PObj *)ctx->caller_ctx;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->caller_ctx);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->lex_pad);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->outer_ctx);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->current_sub);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->handlers);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->current_cont);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->current_object);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->current_namespace);
+        Parrot_gc_mark_PMC_alive(INTERP, ctx->results_signature);
 
-        obj = (PObj *)ctx->lex_pad;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->outer_ctx;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->current_sub;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->handlers;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->current_cont;
-        if (obj && !PObj_live_TEST(obj))
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->current_object;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->current_namespace;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
-        obj = (PObj *)ctx->results_signature;
-        if (obj)
-            Parrot_gc_mark_PObj_alive(interp, obj);
-
         if (!ctx->n_regs_used)
             return;
 
Index: src/vtables.c
===================================================================
--- src/vtables.c	(revision 41448)
+++ src/vtables.c	(revision 41449)
@@ -212,16 +212,11 @@
         if (!vtable)
             continue;
 
-        if (vtable->mro)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)vtable->mro);
-        if (vtable->_namespace)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)vtable->_namespace);
-        if (vtable->whoami)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)vtable->whoami);
-        if (vtable->provides_str)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)vtable->provides_str);
-        if (vtable->pmc_class)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)vtable->pmc_class);
+        Parrot_gc_mark_PMC_alive(interp, vtable->mro);
+        Parrot_gc_mark_PMC_alive(interp, vtable->_namespace);
+        Parrot_gc_mark_STRING_alive(interp, vtable->whoami);
+        Parrot_gc_mark_STRING_alive(interp, vtable->provides_str);
+        Parrot_gc_mark_PMC_alive(interp, vtable->pmc_class);
     }
 }
 
Index: src/gc/gc_ms.c
===================================================================
--- src/gc/gc_ms.c	(revision 41448)
+++ src/gc/gc_ms.c	(revision 41449)
@@ -222,7 +222,7 @@
     /* keep the scheduler and its kids alive for Task-like PMCs to destroy
      * themselves; run a sweep to collect them */
     if (interp->scheduler) {
-        Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->scheduler);
+        Parrot_gc_mark_PMC_alive(interp, interp->scheduler);
         VTABLE_mark(interp, interp->scheduler);
         Parrot_gc_sweep_pool(interp, interp->mem_pools->pmc_pool);
     }
Index: src/gc/mark_sweep.c
===================================================================
--- src/gc/mark_sweep.c	(revision 41448)
+++ src/gc/mark_sweep.c	(revision 41449)
@@ -188,7 +188,7 @@
     }
 
     /* mark the list of iglobals */
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->iglobals);
+    Parrot_gc_mark_PMC_alive(interp, interp->iglobals);
 
     /* mark the current continuation */
     obj = (PObj *)interp->current_cont;
@@ -196,20 +196,19 @@
         Parrot_gc_mark_PObj_alive(interp, obj);
 
     /* mark the current context. */
-    Parrot_gc_mark_PObj_alive(interp, (PObj*)CURRENT_CONTEXT(interp));
+    Parrot_gc_mark_PMC_alive(interp, CURRENT_CONTEXT(interp));
 
     /* mark the dynamic environment. */
-    Parrot_gc_mark_PObj_alive(interp, (PObj*)interp->dynamic_env);
+    Parrot_gc_mark_PMC_alive(interp, interp->dynamic_env);
 
     /* mark the vtables: the data, Class PMCs, etc. */
     mark_vtables(interp);
 
     /* mark the root_namespace */
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->root_namespace);
+    Parrot_gc_mark_PMC_alive(interp, interp->root_namespace);
 
     /* mark the concurrency scheduler */
-    if (interp->scheduler)
-        Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->scheduler);
+    Parrot_gc_mark_PMC_alive(interp, interp->scheduler);
 
     /* s. packfile.c */
     mark_const_subs(interp);
@@ -218,15 +217,15 @@
     mark_object_cache(interp);
 
     /* Now mark the class hash */
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->class_hash);
+    Parrot_gc_mark_PMC_alive(interp, interp->class_hash);
 
     /* Now mark the HLL stuff */
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->HLL_info);
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->HLL_namespace);
+    Parrot_gc_mark_PMC_alive(interp, interp->HLL_info);
+    Parrot_gc_mark_PMC_alive(interp, interp->HLL_namespace);
 
     /* Mark the registry */
     PARROT_ASSERT(interp->gc_registry);
-    Parrot_gc_mark_PObj_alive(interp, (PObj *)interp->gc_registry);
+    Parrot_gc_mark_PMC_alive(interp, interp->gc_registry);
 
     /* Mark the MMD cache. */
     if (interp->op_mmd_cache)
@@ -546,10 +545,9 @@
             PObj_high_priority_gc_CLEAR(current);
 
         /* mark properties */
-        if (PMC_metadata(current))
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)PMC_metadata(current));
+        Parrot_gc_mark_PMC_alive(interp, PMC_metadata(current));
 
-         if (PObj_custom_mark_TEST(current)) {
+        if (PObj_custom_mark_TEST(current)) {
             PARROT_ASSERT(!PObj_on_free_list_TEST(current));
             VTABLE_mark(interp, current);
         }
Index: src/dynpmc/dynlexpad.pmc
===================================================================
--- src/dynpmc/dynlexpad.pmc	(revision 41448)
+++ src/dynpmc/dynlexpad.pmc	(revision 41449)
@@ -200,8 +200,7 @@
 
     VTABLE void mark() {
         PMC *std_pad = PARROT_DYNLEXPAD(SELF)->init;
-        if (std_pad)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)std_pad);
+        Parrot_gc_mark_PMC_alive(INTERP, std_pad);
         if (PARROT_DYNLEXPAD(SELF)->hash)
             parrot_mark_hash(interp, PARROT_DYNLEXPAD(SELF)->hash);
     }
Index: src/packfile.c
===================================================================
--- src/packfile.c	(revision 41448)
+++ src/packfile.c	(revision 41449)
@@ -805,13 +805,11 @@
             case PFC_PMC:
             case PFC_KEY:
                 pmc = constants[i]->u.key;
-                if (pmc)
-                    Parrot_gc_mark_PObj_alive(interp, (PObj *)pmc);
+                Parrot_gc_mark_PMC_alive(interp, pmc);
                 break;
             case PFC_STRING:
                 string = constants[i]->u.string;
-                if (string)
-                    Parrot_gc_mark_PObj_alive(interp, (PObj *)string);
+                Parrot_gc_mark_STRING_alive(interp, string);
                 break;
             default:
                 /* Do nothing. */
Index: src/io/core.c
===================================================================
--- src/io/core.c	(revision 41448)
+++ src/io/core.c	(revision 41449)
@@ -125,9 +125,7 @@
      * to be kept alive AFAIK -leo
      */
     for (i = 0; i < 3; i++) {
-        if (table[i]) {
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)table[i]);
-        }
+        Parrot_gc_mark_PMC_alive(interp, table[i]);
     }
 }
 
Index: src/key.c
===================================================================
--- src/key.c	(revision 41448)
+++ src/key.c	(revision 41449)
@@ -612,17 +612,13 @@
     if (flags == KEY_string_FLAG) {
         STRING *str_key;
         GETATTR_Key_str_key(interp, key, str_key);
-
-        /* XXX str_key can be NULL from GETATTR_Key_str_key, */
-        /* so shouldn't be marked. */
-        Parrot_gc_mark_PObj_alive(interp, (PObj *)str_key);
+        Parrot_gc_mark_STRING_alive(interp, str_key);
     }
 
     /* Mark next key */
     if ((flags == KEY_string_FLAG) || (flags == KEY_pmc_FLAG)) {
         GETATTR_Key_next_key(interp, key, next_key);
-        if (next_key)
-            Parrot_gc_mark_PObj_alive(interp, (PObj *)next_key);
+        Parrot_gc_mark_PMC_alive(interp, next_key);
     }
 
 }