diff --git a/src/gc/alloc_resources.c b/src/gc/alloc_resources.c
index 6930bb8..4468512 100644
--- a/src/gc/alloc_resources.c
+++ b/src/gc/alloc_resources.c
@@ -724,8 +724,7 @@ free_old_mem_blocks(
         else {
             /* Note that we don't have it any more */
             mem_pools->memory_allocated -= cur_block->size;
-            mem_pools->memory_used -=
-                cur_block->size - cur_block->free - cur_block->freed;
+            mem_pools->memory_used -= cur_block->size - cur_block->free;
 
             /* We know the pool body and pool header are a single chunk, so
              * this is enough to get rid of 'em both */
diff --git a/src/gc/gc_ms.c b/src/gc/gc_ms.c
index 08b2cce..cc9aac2 100644
--- a/src/gc/gc_ms.c
+++ b/src/gc/gc_ms.c
@@ -1268,7 +1268,6 @@ gc_ms_reallocate_string_storage(PARROT_INTERP, ARGMOD(STRING *str),
     /* Decrease usage */
     PARROT_ASSERT(Buffer_pool(str));
     Buffer_pool(str)->freed += old_size;
-    interp->mem_pools->memory_used -= old_size;
 
     /* copy mem from strstart, *not* bufstart */
     oldmem             = str->strstart;
diff --git a/src/gc/mark_sweep.c b/src/gc/mark_sweep.c
index 92bbb3c..b6baba6 100644
--- a/src/gc/mark_sweep.c
+++ b/src/gc/mark_sweep.c
@@ -32,13 +32,11 @@ throughout the rest of Parrot.
 /* Don't modify between HEADERIZER BEGIN / HEADERIZER END.  Your changes will be lost. */
 
 static void free_buffer(SHIM_INTERP,
-    ARGMOD(Memory_Pools *mem_pools),
+    SHIM(Memory_Pools *mem_pools),
     ARGMOD(Fixed_Size_Pool *pool),
     ARGMOD(Buffer *b))
-        __attribute__nonnull__(2)
         __attribute__nonnull__(3)
         __attribute__nonnull__(4)
-        FUNC_MODIFIES(*mem_pools)
         FUNC_MODIFIES(*pool)
         FUNC_MODIFIES(*b);
 
@@ -80,8 +78,7 @@ static Fixed_Size_Pool * new_string_pool(PARROT_INTERP,
         FUNC_MODIFIES(*mem_pools);
 
 #define ASSERT_ARGS_free_buffer __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
-       PARROT_ASSERT_ARG(mem_pools) \
-    , PARROT_ASSERT_ARG(pool) \
+       PARROT_ASSERT_ARG(pool) \
     , PARROT_ASSERT_ARG(b))
 #define ASSERT_ARGS_free_pmc_in_pool __attribute__unused__ int _ASSERT_ARGS_CHECK = (\
        PARROT_ASSERT_ARG(interp) \
@@ -668,7 +665,7 @@ reuse later.
 
 static void
 free_buffer(SHIM_INTERP,
-        ARGMOD(Memory_Pools *mem_pools),
+        SHIM(Memory_Pools *mem_pools),
         ARGMOD(Fixed_Size_Pool *pool),
         ARGMOD(Buffer *b))
 {
@@ -693,9 +690,7 @@ free_buffer(SHIM_INTERP,
 
             /* We can have shared buffers. Don't count them (yet) */
             if (!(*buffer_flags & Buffer_shared_FLAG)) {
-                size_t size = ALIGNED_STRING_SIZE(Buffer_buflen(b));
-                block->freed += size;
-                mem_pools->memory_used -= size;
+                block->freed  += ALIGNED_STRING_SIZE(Buffer_buflen(b));
             }
 
         }