diff --git a/include/jemalloc/internal/pa.h b/include/jemalloc/internal/pa.h
index ef140b3e..a4f80818 100644
--- a/include/jemalloc/internal/pa.h
+++ b/include/jemalloc/internal/pa.h
@@ -122,8 +122,7 @@ size_t pa_shard_extent_sn_next(pa_shard_t *shard);
 edata_t *pa_alloc(tsdn_t *tsdn, pa_shard_t *shard, size_t size,
     size_t alignment, bool slab, szind_t szind, bool *zero, size_t *mapped_add);
 /* Returns true on error, in which case nothing changed. */
-bool
-pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata, size_t new_usize,
-    szind_t szind, bool slab, bool *zero, size_t *mapped_add);
+bool pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata, size_t old_size,
+    size_t new_size, szind_t szind, bool slab, bool *zero, size_t *mapped_add);
 
 #endif /* JEMALLOC_INTERNAL_PA_H */
diff --git a/src/large.c b/src/large.c
index 60b51d8c..c01b0577 100644
--- a/src/large.c
+++ b/src/large.c
@@ -106,7 +106,9 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, edata_t *edata, size_t usize,
 		zero = true;
 	}
 
+	size_t old_size = edata_size_get(edata);
 	size_t old_usize = edata_usize_get(edata);
+	size_t new_size = usize + sz_large_pad;
 
 	/*
 	 * Copy zero into is_zeroed_trail and pass the copy when allocating the
@@ -116,7 +118,7 @@ large_ralloc_no_move_expand(tsdn_t *tsdn, edata_t *edata, size_t usize,
 	bool is_zeroed_trail = zero;
 	size_t mapped_add;
 	szind_t szind = sz_size2index(usize);
-	bool err = pa_expand(tsdn, &arena->pa_shard, edata, usize,
+	bool err = pa_expand(tsdn, &arena->pa_shard, edata, old_size, new_size,
 	    szind, /* slab */ false, &is_zeroed_trail, &mapped_add);
 	if (err) {
 		return true;
diff --git a/src/pa.c b/src/pa.c
index 7fafa7e3..8f33d9a4 100644
--- a/src/pa.c
+++ b/src/pa.c
@@ -96,29 +96,31 @@ pa_alloc(tsdn_t *tsdn, pa_shard_t *shard, size_t size, size_t alignment,
 }
 
 bool
-pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata, size_t new_usize,
-    szind_t szind, bool slab, bool *zero, size_t *mapped_add) {
+pa_expand(tsdn_t *tsdn, pa_shard_t *shard, edata_t *edata, size_t old_size,
+    size_t new_size, szind_t szind, bool slab, bool *zero, size_t *mapped_add) {
+	assert(new_size > old_size);
+
 	ehooks_t *ehooks = pa_shard_ehooks_get(shard);
-	size_t old_usize = edata_usize_get(edata);
-	size_t trail_size = new_usize - old_usize;
 	void *trail_begin = edata_past_get(edata);
+	size_t expand_amount = new_size - old_size;
 
 	*mapped_add = 0;
 	if (ehooks_merge_will_fail(ehooks)) {
 		return true;
 	}
 	edata_t *trail = ecache_alloc(tsdn, shard, ehooks, &shard->ecache_dirty,
-	    trail_begin, trail_size, PAGE, /* slab */ false, SC_NSIZES, zero);
+	    trail_begin, expand_amount, PAGE, /* slab */ false, SC_NSIZES,
+	    zero);
 	if (trail == NULL) {
 		trail = ecache_alloc(tsdn, shard, ehooks, &shard->ecache_muzzy,
-		    trail_begin, trail_size, PAGE, /* slab */ false, SC_NSIZES,
-		    zero);
+		    trail_begin, expand_amount, PAGE, /* slab */ false,
+		    SC_NSIZES, zero);
 	}
 	if (trail == NULL) {
 		trail = ecache_alloc_grow(tsdn, shard, ehooks,
-		    &shard->ecache_retained, trail_begin, trail_size, PAGE,
+		    &shard->ecache_retained, trail_begin, expand_amount, PAGE,
 		    /* slab */ false, SC_NSIZES, zero);
-		*mapped_add = trail_size;
+		*mapped_add = expand_amount;
 	}
 	if (trail == NULL) {
 		*mapped_add = 0;