diff --git a/.github/workflows/CI.yml b/.github/workflows/CI.yml
index 94cbedd3e..c60296707 100644
--- a/.github/workflows/CI.yml
+++ b/.github/workflows/CI.yml
@@ -6,21 +6,18 @@ on:
     - master
   pull_request: {}
 
+env:
+  MSRV: 1.49.0
+
 jobs:
-  check:
+  check-stable:
+    # Run `cargo check` first to ensure that the pushed code at least compiles.
     runs-on: ubuntu-latest
-    strategy:
-      # Disable fail-fast. If the test run for a particular Rust version fails,
-      # don't cancel the other test runs, so that we can determine whether a
-      # failure only occurs on a particular version.
-      fail-fast: false
-      matrix:
-        rust: [stable, 1.49.0]
     steps:
     - uses: actions/checkout@master
     - uses: actions-rs/toolchain@v1
       with:
-        toolchain: ${{ matrix.rust }}
+        toolchain: stable
         profile: minimal
         override: true
     - name: Check
@@ -43,6 +40,33 @@ jobs:
         RUSTDOCFLAGS: "-D rustdoc::broken_intra_doc_links"
       run: cargo doc --all-features --no-deps
 
+  check-msrv:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: "install Rust ${{ env.MSRV }}"
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: ${{ env.MSRV }}
+        profile: minimal
+    - name: "install Rust nightly"
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: nightly
+        profile: minimal
+    - name: Select minimal versions
+      uses: actions-rs/cargo@v1
+      with:
+        command: update
+        args: -Z minimal-versions
+        toolchain: nightly
+    - name: Check
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: --all --all-targets --all-features --locked
+        toolchain: ${{ env.MSRV }}
+
   cargo-hack:
     runs-on: ubuntu-latest
     steps:
@@ -51,16 +75,15 @@ jobs:
       with:
         toolchain: stable
         profile: minimal
-    - name: Install cargo-hack
-      run: |
-        curl -LsSf https://github.com/taiki-e/cargo-hack/releases/latest/download/cargo-hack-x86_64-unknown-linux-gnu.tar.gz | tar xzf - -C ~/.cargo/bin
+    - name: install cargo-hack
+      uses: taiki-e/install-action@cargo-hack
     - name: cargo hack check
       working-directory: ${{ matrix.subcrate }}
       run: cargo hack check --each-feature --no-dev-deps --workspace
 
   test-versions:
     # Test against the stable, beta, and nightly Rust toolchains on ubuntu-latest.
-    needs: check
+    needs: check-stable
     runs-on: ubuntu-latest
     strategy:
       # Disable fail-fast. If the test run for a particular Rust version fails,
@@ -68,10 +91,11 @@ jobs:
       # failure only occurs on a particular version.
       fail-fast: false
       matrix:
-        rust: [stable, beta, nightly, 1.49.0]
+        rust: [stable, beta, nightly]
     steps:
     - uses: actions/checkout@master
-    - uses: actions-rs/toolchain@v1
+    - name: "install Rust ${{ matrix.rust }}"
+      uses: actions-rs/toolchain@v1
       with:
         toolchain: ${{ matrix.rust }}
         profile: minimal
@@ -82,8 +106,36 @@ jobs:
         command: test
         args: --workspace --all-features
 
+  test-msrv:
+    needs: check-msrv
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: "install Rust ${{ env.MSRV }}"
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: ${{ env.MSRV }}
+        profile: minimal
+    - name: "install Rust nightly"
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: nightly
+        profile: minimal
+    - name: Select minimal versions
+      uses: actions-rs/cargo@v1
+      with:
+        command: update
+        args: -Z minimal-versions
+        toolchain: nightly
+    - name: test
+      uses: actions-rs/cargo@v1
+      with:
+        command: check
+        args: --workspace --all-features --locked
+        toolchain: ${{ env.MSRV }}
+
   style:
-    needs: check
+    needs: check-stable
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@master
diff --git a/tower/Cargo.toml b/tower/Cargo.toml
index f6407a4ea..f80b7b1fb 100644
--- a/tower/Cargo.toml
+++ b/tower/Cargo.toml
@@ -70,7 +70,7 @@ 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 }
+hdrhistogram = { version = "7.0", optional = true, default-features = false }
 indexmap = { version = "1.0.2", optional = true }
 rand = { version = "0.8", features = ["small_rng"], optional = true }
 slab = { version = "0.4", optional = true }
@@ -82,14 +82,15 @@ pin-project-lite = { version = "0.2.7", optional = true }
 
 [dev-dependencies]
 futures = "0.3"
-hdrhistogram = "7.0"
+hdrhistogram = { version = "7.0", default-features = false }
 pin-project-lite = "0.2.7"
-tokio = { version = "1.6", features = ["macros", "sync", "test-util", "rt-multi-thread"] }
+tokio = { version = "1.6.2", features = ["macros", "sync", "test-util", "rt-multi-thread"] }
 tokio-stream = "0.1"
 tokio-test = "0.4"
 tower-test = { version = "0.4", path = "../tower-test" }
-tracing-subscriber = "0.2.14"
+tracing-subscriber = { version = "0.3", default-features = false, features = ["fmt", "ansi"] }
 http = "0.2"
+lazy_static = "1.4.0"
 
 [package.metadata.docs.rs]
 all-features = true