diff --git a/apps/emqx_auth_mongo/rebar.config b/apps/emqx_auth_mongo/rebar.config
index 834bff904..f44e69543 100644
--- a/apps/emqx_auth_mongo/rebar.config
+++ b/apps/emqx_auth_mongo/rebar.config
@@ -1,5 +1,13 @@
 {deps,
- [{mongodb, {git,"https://github.com/emqx/mongodb-erlang", {tag, "v3.0.7"}}}
+  %% NOTE: mind poolboy version when updating mongodb-erlang version
+ [{mongodb, {git,"https://github.com/emqx/mongodb-erlang", {tag, "v3.0.7"}}},
+  %% mongodb-erlang uses a special fork https://github.com/comtihon/poolboy.git
+  %% (which has overflow_ttl feature added).
+  %% However, it references `{branch, "master}` (commit 9c06a9a on 2021-04-07).
+  %% By accident, We have always been using the upstream fork due to
+  %% eredis_cluster's dependency getting resolved earlier.
+  %% Here we pin 1.5.2 to avoid surprises in the future.
+  {poolboy, {git, "https://github.com/emqx/poolboy.git", {tag, "1.5.2"}}}
  ]}.
 
 {edoc_opts, [{preprocess, true}]}.
diff --git a/apps/emqx_auth_redis/rebar.config b/apps/emqx_auth_redis/rebar.config
index 72c91aa4e..528ffbeb4 100644
--- a/apps/emqx_auth_redis/rebar.config
+++ b/apps/emqx_auth_redis/rebar.config
@@ -1,5 +1,8 @@
 {deps,
- [{eredis_cluster, {git, "https://github.com/emqx/eredis_cluster", {tag, "0.6.4"}}}
+  %% NOTE: mind poolboy version when updating eredis_cluster version
+  %% poolboy version may clash with emqx_auth_mongo
+ [{eredis_cluster, {git, "https://github.com/emqx/eredis_cluster", {tag, "0.6.4"}}},
+  {poolboy, {git, "https://github.com/emqx/poolboy.git", {tag, "1.5.2"}}}
  ]}.
 
 {erl_opts, [warn_unused_vars,