diff --git a/include/jemalloc/internal/ecache.h b/include/jemalloc/internal/ecache.h
index 8532192c..a11418c0 100644
--- a/include/jemalloc/internal/ecache.h
+++ b/include/jemalloc/internal/ecache.h
@@ -10,6 +10,8 @@ struct ecache_s {
 	eset_t eset;
 	/* All stored extents must be in the same state. */
 	extent_state_t state;
+	/* The index of the ehooks the ecache is associated with. */
+	unsigned ind;
 	/*
 	 * If true, delay coalescing until eviction; otherwise coalesce during
 	 * deallocation.
@@ -52,8 +54,13 @@ ecache_nbytes_get(ecache_t *ecache, pszind_t ind) {
 	return eset_nbytes_get(&ecache->eset, ind);
 }
 
+static inline unsigned
+ecache_ind_get(ecache_t *ecache) {
+	return ecache->ind;
+}
+
 bool ecache_init(tsdn_t *tsdn, ecache_t *ecache, extent_state_t state,
-    bool delay_coalesce);
+    unsigned ind, bool delay_coalesce);
 void ecache_prefork(tsdn_t *tsdn, ecache_t *ecache);
 void ecache_postfork_parent(tsdn_t *tsdn, ecache_t *ecache);
 void ecache_postfork_child(tsdn_t *tsdn, ecache_t *ecache);
diff --git a/src/arena.c b/src/arena.c
index b5c8606f..e795acf2 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -2018,14 +2018,16 @@ 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 (ecache_init(tsdn, &arena->ecache_dirty, extent_state_dirty, true)) {
+	if (ecache_init(tsdn, &arena->ecache_dirty, extent_state_dirty, ind,
+	    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 (ecache_init(tsdn, &arena->ecache_muzzy, extent_state_muzzy, false)) {
+	if (ecache_init(tsdn, &arena->ecache_muzzy, extent_state_muzzy, ind,
+	    false)) {
 		goto label_error;
 	}
 	/*
@@ -2035,7 +2037,7 @@ arena_new(tsdn_t *tsdn, unsigned ind, extent_hooks_t *extent_hooks) {
 	 * in the critical path.
 	 */
 	if (ecache_init(tsdn, &arena->ecache_retained, extent_state_retained,
-	    false)) {
+	    ind, false)) {
 		goto label_error;
 	}
 
diff --git a/src/ecache.c b/src/ecache.c
index a57a0a6f..301b7ca6 100644
--- a/src/ecache.c
+++ b/src/ecache.c
@@ -2,13 +2,14 @@
 #include "jemalloc/internal/jemalloc_internal_includes.h"
 
 bool
-ecache_init(tsdn_t *tsdn, ecache_t *ecache, extent_state_t state,
+ecache_init(tsdn_t *tsdn, ecache_t *ecache, extent_state_t state, unsigned ind,
     bool delay_coalesce) {
 	if (malloc_mutex_init(&ecache->mtx, "extents", WITNESS_RANK_EXTENTS,
 	    malloc_mutex_rank_exclusive)) {
 		return true;
 	}
 	ecache->state = state;
+	ecache->ind = ind;
 	ecache->delay_coalesce = delay_coalesce;
 	eset_init(&ecache->eset, state);
 	return false;
diff --git a/src/extent2.c b/src/extent2.c
index 1b70f202..1dbccf6e 100644
--- a/src/extent2.c
+++ b/src/extent2.c
@@ -1062,6 +1062,8 @@ extent_alloc_wrapper(tsdn_t *tsdn, arena_t *arena, ehooks_t *ehooks,
 static bool
 extent_can_coalesce(ecache_t *ecache, const edata_t *inner,
     const edata_t *outer) {
+	assert(edata_arena_ind_get(inner) == ecache_ind_get(ecache));
+
 	if (edata_arena_ind_get(inner) != edata_arena_ind_get(outer)) {
 		return false;
 	}