diff --git a/mozilla/nsprpub/lib/ds/plarena.c b/mozilla/nsprpub/lib/ds/plarena.c
index cc2ffb00a89..40531951453 100644
--- a/mozilla/nsprpub/lib/ds/plarena.c
+++ b/mozilla/nsprpub/lib/ds/plarena.c
@@ -346,14 +346,14 @@ PR_IMPLEMENT(void) PL_ArenaFinish(void)
 }
 
 PR_IMPLEMENT(size_t) PL_SizeOfArenaPoolExcludingPool(
-    PLArenaPool *pool, PLMallocSizeFn mallocSizeOf)
+    const PLArenaPool *pool, PLMallocSizeFn mallocSizeOf)
 {
     /*
      * The first PLArena is within |pool|, so don't measure it.  Subsequent
-     * PLArenas are separate and must measured.
+     * PLArenas are separate and must be measured.
      */
     size_t size = 0;
-    PLArena *arena = pool->first.next;
+    const PLArena *arena = pool->first.next;
     while (arena) {
         size += mallocSizeOf(arena);
         arena = arena->next;
diff --git a/mozilla/nsprpub/lib/ds/plarenas.h b/mozilla/nsprpub/lib/ds/plarenas.h
index 4cbe32c4c39..f4a00cd1b82 100644
--- a/mozilla/nsprpub/lib/ds/plarenas.h
+++ b/mozilla/nsprpub/lib/ds/plarenas.h
@@ -61,17 +61,17 @@ PR_EXTERN(void) PL_ArenaRelease(PLArenaPool *pool, char *mark);
 PR_EXTERN(void) PL_ClearArenaPool(PLArenaPool *pool, PRInt32 pattern);
 
 /*
-** A function like malloc_size() or malloc_usable_size() that returns the
+** A function like malloc_size() or malloc_usable_size() that measures the
 ** size of a heap block.
 */
 typedef size_t (*PLMallocSizeFn)(const void *ptr);
 
 /*
-** Return all memory used by a PLArenaPool, excluding the PLArenaPool
+** Measure all memory used by a PLArenaPool, excluding the PLArenaPool
 ** structure.
 */
 PR_EXTERN(size_t) PL_SizeOfArenaPoolExcludingPool(
-    PLArenaPool *pool, PLMallocSizeFn mallocSizeOf);
+    const PLArenaPool *pool, PLMallocSizeFn mallocSizeOf);
 
 PR_END_EXTERN_C