diff --git a/include/jemalloc/internal/eset.h b/include/jemalloc/internal/eset.h
index 1c18f4ee..55db75e1 100644
--- a/include/jemalloc/internal/eset.h
+++ b/include/jemalloc/internal/eset.h
@@ -6,6 +6,9 @@
 #include "jemalloc/internal/extent.h"
 #include "jemalloc/internal/mutex.h"
 
+/* This is a transitional declarion, while we move extent.c into eset.c. */
+extern const bitmap_info_t eset_bitmap_info;
+
 /*
  * An eset ("extent set") is a quantized collection of extents, with built-in
  * LRU queue.
@@ -57,4 +60,7 @@ struct eset_s {
 	bool delay_coalesce;
 };
 
+bool eset_init(tsdn_t *tsdn, eset_t *eset, extent_state_t state,
+    bool delay_coalesce);
+
 #endif /* JEMALLOC_INTERNAL_ESET_H */
diff --git a/include/jemalloc/internal/extent_externs.h b/include/jemalloc/internal/extent_externs.h
index 45271d7c..7a223840 100644
--- a/include/jemalloc/internal/extent_externs.h
+++ b/include/jemalloc/internal/extent_externs.h
@@ -27,8 +27,6 @@ size_t extent_size_quantize_ceil(size_t size);
 ph_proto(, extent_avail_, extent_tree_t, extent_t)
 ph_proto(, extent_heap_, extent_heap_t, extent_t)
 
-bool extents_init(tsdn_t *tsdn, eset_t *eset, extent_state_t state,
-    bool delay_coalesce);
 extent_state_t extents_state_get(const eset_t *eset);
 size_t extents_npages_get(eset_t *eset);
 /* Get the number of extents in the given page size index. */
diff --git a/src/arena.c b/src/arena.c
index 5380deed..1d269dc7 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -2022,16 +2022,14 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 * are likely to be reused soon after deallocation, and the cost of
 	 * merging/splitting extents is non-trivial.
 	 */
-	if (extents_init(tsdn, &arena->extents_dirty, extent_state_dirty,
-	    true)) {
+	if (eset_init(tsdn, &arena->extents_dirty, extent_state_dirty, true)) {
 		goto label_error;
 	}
 	/*
 	 * Coalesce muzzy extents immediately, because operations on them are in
 	 * the critical path much less often than for dirty extents.
 	 */
-	if (extents_init(tsdn, &arena->extents_muzzy, extent_state_muzzy,
-	    false)) {
+	if (eset_init(tsdn, &arena->extents_muzzy, extent_state_muzzy, false)) {
 		goto label_error;
 	}
 	/*
@@ -2040,7 +2038,7 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 * coalescing), but also because operations on retained extents are not
 	 * in the critical path.
 	 */
-	if (extents_init(tsdn, &arena->extents_retained, extent_state_retained,
+	if (eset_init(tsdn, &arena->extents_retained, extent_state_retained,
 	    false)) {
 		goto label_error;
 	}
diff --git a/src/eset.c b/src/eset.c
index 3b8d1cbc..09148d0c 100644
--- a/src/eset.c
+++ b/src/eset.c
@@ -2,3 +2,24 @@
 #include "jemalloc/internal/jemalloc_internal_includes.h"
 
 #include "jemalloc/internal/eset.h"
+
+const bitmap_info_t eset_bitmap_info =
+    BITMAP_INFO_INITIALIZER(SC_NPSIZES+1);
+
+bool
+eset_init(tsdn_t *tsdn, eset_t *eset, extent_state_t state,
+    bool delay_coalesce) {
+	if (malloc_mutex_init(&eset->mtx, "extents", WITNESS_RANK_EXTENTS,
+	    malloc_mutex_rank_exclusive)) {
+		return true;
+	}
+	for (unsigned i = 0; i < SC_NPSIZES + 1; i++) {
+		extent_heap_new(&eset->heaps[i]);
+	}
+	bitmap_init(eset->bitmap, &eset_bitmap_info, true);
+	extent_list_init(&eset->lru);
+	atomic_store_zu(&eset->npages, 0, ATOMIC_RELAXED);
+	eset->state = state;
+	eset->delay_coalesce = delay_coalesce;
+	return false;
+}
diff --git a/src/extent.c b/src/extent.c
index d5350142..51a145df 100644
--- a/src/extent.c
+++ b/src/extent.c
@@ -19,9 +19,6 @@ mutex_pool_t	extent_mutex_pool;
 
 size_t opt_lg_extent_max_active_fit = LG_EXTENT_MAX_ACTIVE_FIT_DEFAULT;
 
-static const bitmap_info_t eset_bitmap_info =
-    BITMAP_INFO_INITIALIZER(SC_NPSIZES+1);
-
 static void *extent_alloc_default(extent_hooks_t *extent_hooks, void *new_addr,
     size_t size, size_t alignment, bool *zero, bool *commit,
     unsigned arena_ind);
@@ -308,24 +305,6 @@ extent_size_quantize_ceil(size_t size) {
 /* Generate pairing heap functions. */
 ph_gen(, extent_heap_, extent_heap_t, extent_t, ph_link, extent_snad_comp)
 
-bool
-extents_init(tsdn_t *tsdn, eset_t *eset, extent_state_t state,
-    bool delay_coalesce) {
-	if (malloc_mutex_init(&eset->mtx, "extents", WITNESS_RANK_EXTENTS,
-	    malloc_mutex_rank_exclusive)) {
-		return true;
-	}
-	for (unsigned i = 0; i < SC_NPSIZES + 1; i++) {
-		extent_heap_new(&eset->heaps[i]);
-	}
-	bitmap_init(eset->bitmap, &eset_bitmap_info, true);
-	extent_list_init(&eset->lru);
-	atomic_store_zu(&eset->npages, 0, ATOMIC_RELAXED);
-	eset->state = state;
-	eset->delay_coalesce = delay_coalesce;
-	return false;
-}
-
 extent_state_t
 extents_state_get(const eset_t *eset) {
 	return eset->state;