diff --git a/Makefile.in b/Makefile.in
index 96c4ae03..aefd6d87 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -162,6 +162,7 @@ TESTS_UNIT := \
 	$(srcroot)test/unit/arena_reset.c \
 	$(srcroot)test/unit/atomic.c \
 	$(srcroot)test/unit/background_thread.c \
+	$(srcroot)test/unit/background_thread_enable.c \
 	$(srcroot)test/unit/base.c \
 	$(srcroot)test/unit/bitmap.c \
 	$(srcroot)test/unit/ckh.c \
diff --git a/src/background_thread.c b/src/background_thread.c
index 6baff22b..a8a5a052 100644
--- a/src/background_thread.c
+++ b/src/background_thread.c
@@ -600,7 +600,8 @@ background_threads_enable(tsd_t *tsd) {
 		    arena_get(tsd_tsdn(tsd), i, false) == NULL) {
 			continue;
 		}
-		background_thread_info_t *info = &background_thread_info[i];
+		background_thread_info_t *info = &background_thread_info[
+		    i % ncpus];
 		malloc_mutex_lock(tsd_tsdn(tsd), &info->mtx);
 		assert(info->state == background_thread_stopped);
 		background_thread_init(tsd, info);
diff --git a/test/unit/background_thread_enable.c b/test/unit/background_thread_enable.c
new file mode 100644
index 00000000..9bb58652
--- /dev/null
+++ b/test/unit/background_thread_enable.c
@@ -0,0 +1,34 @@
+#include "test/jemalloc_test.h"
+
+const char *malloc_conf = "background_thread:false,narenas:1";
+
+TEST_BEGIN(test_deferred) {
+	test_skip_if(!have_background_thread);
+
+	unsigned id;
+	size_t sz_u = sizeof(unsigned);
+
+	/*
+	 * 10 here is somewhat arbitrary, except insofar as we want to ensure
+	 * that the number of background threads is smaller than the number of
+	 * arenas.  I'll ragequit long before we have to spin up 10 threads per
+	 * cpu to handle background purging, so this is a conservative
+	 * approximation.
+	 */
+	for (unsigned i = 0; i < 10 * ncpus; i++) {
+		assert_d_eq(mallctl("arenas.create", &id, &sz_u, NULL, 0), 0,
+		    "Failed to create arena");
+	}
+
+	bool enable = true;
+	size_t sz_b = sizeof(bool);
+	assert_d_eq(mallctl("background_thread", NULL, NULL, &enable, sz_b), 0,
+	    "Failed to enable background threads");
+}
+TEST_END
+
+int
+main(void) {
+	return test_no_reentrancy(
+	    test_deferred);
+}