diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 971e28032c..e82ce1bc8e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -185,6 +185,7 @@ jobs:
           - x86_64-apple-darwin
           - x86_64-unknown-linux-musl
           - x86_64-unknown-linux-gnu
+          - s390x-unknown-linux-gnu
 
         mode:
           - # debug
@@ -261,6 +262,9 @@ jobs:
           - target: x86_64-unknown-linux-gnu
             host_os: ubuntu-22.04
 
+          - target: s390x-unknown-linux-gnu
+            host_os: ubuntu-22.04
+
     steps:
       - if: ${{ contains(matrix.host_os, 'ubuntu') }}
         run: sudo apt-get update -y
@@ -333,6 +337,7 @@ jobs:
           - aarch64-unknown-linux-musl
           - i686-pc-windows-msvc
           - x86_64-unknown-linux-gnu
+          - s390x-unknown-linux-gnu
 
         mode:
           - # debug
@@ -354,6 +359,9 @@ jobs:
           - target: x86_64-unknown-linux-gnu
             host_os: ubuntu-22.04
 
+          - target: s390x-unknown-linux-gnu
+            host_os: ubuntu-22.04
+
     steps:
       - if: ${{ contains(matrix.host_os, 'ubuntu') }}
         run: sudo apt-get update -y
@@ -485,6 +493,7 @@ jobs:
           - aarch64-unknown-linux-gnu
           - i686-unknown-linux-gnu
           - x86_64-unknown-linux-musl
+          - s390x-unknown-linux-gnu
 
         mode:
           - # debug
@@ -510,6 +519,9 @@ jobs:
           - target: x86_64-unknown-linux-musl
             host_os: ubuntu-22.04
 
+          - target: s390x-unknown-linux-gnu
+            host_os: ubuntu-22.04
+
           # TODO: Add an ARM target after
           # https://github.com/rust-lang/rust/issues/79555 is fixed. This may
           # require https://github.com/rust-lang/rust/issues/79555 to be fixed
diff --git a/include/ring-core/target.h b/include/ring-core/target.h
index 5b46611550..264e7df731 100644
--- a/include/ring-core/target.h
+++ b/include/ring-core/target.h
@@ -40,6 +40,9 @@
 #elif defined(__MIPSEL__) && defined(__LP64__)
 #define OPENSSL_64_BIT
 #define OPENSSL_MIPS64
+#elif defined(__s390x__)
+#define OPENSSL_64_BIT
+#define OPENSSL_S390X
 #elif defined(__wasm__)
 #define OPENSSL_32_BIT
 #else
diff --git a/mk/cargo.sh b/mk/cargo.sh
index d990220279..6cfe12bcbb 100755
--- a/mk/cargo.sh
+++ b/mk/cargo.sh
@@ -21,6 +21,7 @@ rustflags_self_contained="-Clink-self-contained=yes -Clinker=rust-lld"
 qemu_aarch64="qemu-aarch64 -L /usr/aarch64-linux-gnu"
 qemu_arm="qemu-arm -L /usr/arm-linux-gnueabihf"
 qemu_mipsel="qemu-mipsel -L /usr/mipsel-linux-gnu"
+qemu_s390x="qemu-s390x -L /usr/s390x-linux-gnu"
 
 # Avoid putting the Android tools in `$PATH` because there are tools in this
 # directory like `clang` that would conflict with the same-named tools that may
@@ -109,6 +110,13 @@ case $target in
       export CARGO_TARGET_X86_64_UNKNOWN_LINUX_MUSL_RUSTFLAGS="$rustflags_self_contained"
     fi
     ;;
+  s390x-unknown-linux-gnu)
+    export CC_s390x_unknown_linux_gnu=clang-$llvm_version
+    export AR_s390x_unknown_linux_gnu=llvm-ar-$llvm_version
+    export CFLAGS_s390x_unknown_linux_gnu="--sysroot=/usr/s390x-linux-gnu"
+    export CARGO_TARGET_S390X_UNKNOWN_LINUX_GNU_LINKER=s390x-linux-gnu-gcc
+    export CARGO_TARGET_S390X_UNKNOWN_LINUX_GNU_RUNNER="$qemu_s390x"
+    ;;
   wasm32-unknown-unknown)
     # The first two are only needed for when the "wasm_c" feature is enabled.
     export CC_wasm32_unknown_unknown=clang-$llvm_version
diff --git a/mk/install-build-tools.sh b/mk/install-build-tools.sh
index 234516f032..12e1d458eb 100755
--- a/mk/install-build-tools.sh
+++ b/mk/install-build-tools.sh
@@ -91,6 +91,14 @@ case $target in
     libc6-dev-mipsel-cross \
     qemu-user
   ;;
+--target=s390x-unknown-linux-gnu)
+  # Clang is needed for code coverage.
+  use_clang=1
+  install_packages \
+    qemu-user \
+    gcc-s390x-linux-gnu \
+    libc6-dev-s390x-cross
+  ;;
 --target=wasm32-unknown-unknown)
   cargo install wasm-bindgen-cli --bin wasm-bindgen-test-runner
   use_clang=1
diff --git a/src/constant_time.rs b/src/constant_time.rs
index 9ccf8f6653..2bed3824e0 100644
--- a/src/constant_time.rs
+++ b/src/constant_time.rs
@@ -40,6 +40,7 @@ mod tests {
     use crate::{bssl, error};
 
     #[test]
+    #[cfg(not(target_arch = "s390x"))] // Triggers a qemu bug before 8.0.3
     fn test_constant_time() -> Result<(), error::Unspecified> {
         prefixed_extern! {
             fn bssl_constant_time_test_main() -> bssl::Result;