diff --git a/.github/workflows/test-suite.yml b/.github/workflows/test-suite.yml
index 1c1e345..72945a3 100644
--- a/.github/workflows/test-suite.yml
+++ b/.github/workflows/test-suite.yml
@@ -23,14 +23,22 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest, windows-latest]
+        features: ["", "ring", "zero_hash_cache", "ring,zero_hash_cache"]
+        # Skip the ring-less builds on macOS ARM where ring is mandatory.
+        exclude:
+        - os: macos-latest
+          features: ""
+        - os: macos-latest
+          features: "zero_hash_cache"
     runs-on: ${{ matrix.os }}
-    name: test-${{ matrix.os }}
+    name: test-${{ matrix.os }}-feat-${{ matrix.features }}
     steps:
     - uses: actions/checkout@v3
     - name: Get latest version of stable Rust
       run: rustup update stable
     - name: Run tests
-      run: cargo test --release
+      run: cargo test --release --no-default-features --features "${{ matrix.features }}"
+  # We use `--skip-clean` to aggregate the coverage from runs with different features.
   coverage:
     runs-on: ubuntu-latest
     name: cargo-tarpaulin
@@ -40,8 +48,14 @@ jobs:
       run: rustup update stable
     - name: Install cargo-tarpaulin
       uses: taiki-e/install-action@cargo-tarpaulin
-    - name: Check code coverage with cargo-tarpaulin
-      run: cargo-tarpaulin --workspace --all-features --out xml
+    - name: Check code coverage with cargo-tarpaulin (no features)
+      run: cargo-tarpaulin --workspace --out xml --no-default-features
+    - name: Check code coverage with cargo-tarpaulin (just `ring` feature)
+      run: cargo-tarpaulin --workspace --out xml --skip-clean --no-default-features --features "ring"
+    - name: Check code coverage with cargo-tarpaulin (just `zero_hash_cache` feature)
+      run: cargo-tarpaulin --workspace --out xml --skip-clean --no-default-features --features "zero_hash_cache"
+    - name: Check code coverage with cargo-tarpaulin (all features)
+      run: cargo-tarpaulin --workspace --out xml --skip-clean --all-features
     - name: Upload to codecov.io
       uses: codecov/codecov-action@v3
       with:
diff --git a/Cargo.toml b/Cargo.toml
index 6f23a8f..3d9131d 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,7 +12,7 @@ categories = ["cryptography::cryptocurrencies"]
 rust-version = "1.80.0"
 
 [dependencies]
-ring = "0.17"
+ring = { version = "0.17", optional = true }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies]
 cpufeatures = "0.2"
@@ -25,5 +25,6 @@ rustc-hex = "2"
 wasm-bindgen-test = "0.3.33"
 
 [features]
-default = ["zero_hash_cache"]
+default = ["zero_hash_cache", "ring"]
 zero_hash_cache = []
+ring = ["dep:ring"]
diff --git a/src/lib.rs b/src/lib.rs
index 06e7e04..b91b431 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -59,8 +59,10 @@ pub trait Sha256 {
 }
 
 /// Implementation of SHA256 using the `ring` crate (fastest on CPUs without SHA extensions).
+#[cfg(feature = "ring")]
 pub struct RingImpl;
 
+#[cfg(feature = "ring")]
 impl Sha256Context for ring::digest::Context {
     fn new() -> Self {
         Self::new(&ring::digest::SHA256)
@@ -77,6 +79,7 @@ impl Sha256Context for ring::digest::Context {
     }
 }
 
+#[cfg(feature = "ring")]
 impl Sha256 for RingImpl {
     type Context = ring::digest::Context;
 
@@ -97,6 +100,7 @@ impl Sha256 for RingImpl {
 pub enum DynamicImpl {
     #[cfg(target_arch = "x86_64")]
     Sha2,
+    #[cfg(feature = "ring")]
     Ring,
 }
 
@@ -119,15 +123,27 @@ impl DynamicImpl {
     /// Choose the best available implementation based on the currently executing CPU.
     #[inline(always)]
     pub fn best() -> Self {
-        #[cfg(target_arch = "x86_64")]
+        #[cfg(all(not(feature = "ring"), not(target_arch = "x86_64")))]
+        {
+            compile_error!("Ring must be enabled on non-x86_64 architectures");
+        }
+
+        #[cfg(all(not(feature = "ring"), target_arch = "x86_64"))]
+        {
+            Self::Sha2
+        }
+
+        #[cfg(all(feature = "ring", target_arch = "x86_64"))]
         if have_sha_extensions() {
             Self::Sha2
         } else {
             Self::Ring
         }
 
-        #[cfg(not(target_arch = "x86_64"))]
-        Self::Ring
+        #[cfg(all(feature = "ring", not(target_arch = "x86_64")))]
+        {
+            Self::Ring
+        }
     }
 }
 
@@ -139,6 +155,7 @@ impl Sha256 for DynamicImpl {
         match self {
             #[cfg(target_arch = "x86_64")]
             Self::Sha2 => Sha2CrateImpl.hash(input),
+            #[cfg(feature = "ring")]
             Self::Ring => RingImpl.hash(input),
         }
     }
@@ -148,6 +165,7 @@ impl Sha256 for DynamicImpl {
         match self {
             #[cfg(target_arch = "x86_64")]
             Self::Sha2 => Sha2CrateImpl.hash_fixed(input),
+            #[cfg(feature = "ring")]
             Self::Ring => RingImpl.hash_fixed(input),
         }
     }
@@ -159,6 +177,7 @@ impl Sha256 for DynamicImpl {
 pub enum DynamicContext {
     #[cfg(target_arch = "x86_64")]
     Sha2(sha2::Sha256),
+    #[cfg(feature = "ring")]
     Ring(ring::digest::Context),
 }
 
@@ -167,6 +186,7 @@ impl Sha256Context for DynamicContext {
         match DynamicImpl::best() {
             #[cfg(target_arch = "x86_64")]
             DynamicImpl::Sha2 => Self::Sha2(Sha256Context::new()),
+            #[cfg(feature = "ring")]
             DynamicImpl::Ring => Self::Ring(Sha256Context::new()),
         }
     }
@@ -175,6 +195,7 @@ impl Sha256Context for DynamicContext {
         match self {
             #[cfg(target_arch = "x86_64")]
             Self::Sha2(ctxt) => Sha256Context::update(ctxt, bytes),
+            #[cfg(feature = "ring")]
             Self::Ring(ctxt) => Sha256Context::update(ctxt, bytes),
         }
     }
@@ -183,6 +204,7 @@ impl Sha256Context for DynamicContext {
         match self {
             #[cfg(target_arch = "x86_64")]
             Self::Sha2(ctxt) => Sha256Context::finalize(ctxt),
+            #[cfg(feature = "ring")]
             Self::Ring(ctxt) => Sha256Context::finalize(ctxt),
         }
     }