diff --git a/rust/Cargo.toml b/rust/Cargo.toml
index 608f7a688f..5ee68d479f 100644
--- a/rust/Cargo.toml
+++ b/rust/Cargo.toml
@@ -68,6 +68,7 @@ tikv-jemallocator = { version = "0.6.1", features = [
 ] }
 tikv-jemalloc-sys = { version = "0.6.1", features = [
     "disable_initial_exec_tls",
+    "stats",
 ] }
 libc = "0.2.186"
 
@@ -75,4 +76,3 @@ libc = "0.2.186"
 blake2 = "0.10.4"
 hex = "0.4.3"
 rustc_version = "0.4.1"
-
diff --git a/synapse/metrics/jemalloc.py b/synapse/metrics/jemalloc.py
index ef0b4905a8..85bfd699f9 100644
--- a/synapse/metrics/jemalloc.py
+++ b/synapse/metrics/jemalloc.py
@@ -106,7 +106,7 @@ class JemallocStats:
         )
 
         if result != 0:
-            raise Exception("Failed to call mallctl")
+            raise Exception(f"Failed to call mallctl {result}")
 
         if input_var is None:
             return None