diff --git a/tower/Cargo.toml b/tower/Cargo.toml
index 96269dc80..71b872256 100644
--- a/tower/Cargo.toml
+++ b/tower/Cargo.toml
@@ -71,7 +71,7 @@ tower-service = { version = "0.3.1", path = "../tower-service" }
 futures-core = { version = "0.3", optional = true }
 futures-util = { version = "0.3", default-features = false, features = ["alloc"], optional = true }
 hdrhistogram = { version = "7.0", optional = true, default-features = false }
-indexmap = { version = "1.0.2", optional = true }
+indexmap = { version = "=2.2.1", optional = true }
 slab = { version = "0.4", optional = true }
 tokio = { version = "1.6", optional = true, features = ["sync"] }
 tokio-stream = { version = "0.1.0", optional = true }