diff --git a/.github/workflows/full_ci.yml b/.github/workflows/full_ci.yml
index 4389a54375ba8..3655d53605073 100644
--- a/.github/workflows/full_ci.yml
+++ b/.github/workflows/full_ci.yml
@@ -19,12 +19,22 @@ jobs:
           i686-unknown-linux-gnu,
           x86_64-unknown-linux-gnu,
         ]
+        bits: [
+          default,
+          32,
+          64
+        ]
+        exclude:
+          - target: x86_64-unknown-linux-gnu
+            bits: 32
+          - target: x86_64-unknown-linux-gnu
+            bits: 64
     steps:
       - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: TARGET=${{ matrix.target }} sh ./ci/install-rust.sh
       - name: Execute run-docker.sh
-        run: LIBC_CI=1 sh ./ci/run-docker.sh ${{ matrix.target }}
+        run: LIBC_CI=1 RUST_LIBC_TIME_BITS=${{ matrix.bits }} sh ./ci/run-docker.sh ${{ matrix.target }}
 
   macos:
     permissions:
@@ -133,12 +143,22 @@ jobs:
           # aren't defined on redox actually.
           # x86_64-unknown-redox,
         ]
+        include:
+          - bits: default
+          - bits: 32
+            target: arm-unknown-linux-gnueabihf
+          - bits: 64
+            target: arm-unknown-linux-gnueabihf
+          - bits: 32
+            target: powerpc-unknown-linux-gnu
+          - bits: 64
+            target: powerpc-unknown-linux-gnu
     steps:
       - uses: actions/checkout@v4
       - name: Setup Rust toolchain
         run: TARGET=${{ matrix.target }} sh ./ci/install-rust.sh
       - name: Execute run-docker.sh
-        run: LIBC_CI=1 sh ./ci/run-docker.sh ${{ matrix.target }}
+        run: LIBC_CI=1 RUST_LIBC_TIME_BITS=${{ matrix.bits }} sh ./ci/run-docker.sh ${{ matrix.target }}
 
   # These targets are tier 3 or otherwise need to have CI build std via -Zbuild-std.
   # Because of this, only the nightly compiler can be used on these targets.
diff --git a/ci/build.sh b/ci/build.sh
index e22b893222312..4809218e1bf96 100644
--- a/ci/build.sh
+++ b/ci/build.sh
@@ -23,6 +23,29 @@ test_target() {
     TARGET="${2}"
     NO_STD="${3}"
 
+    if [ "$RUST_LIBC_TIME_BITS" = "" ]; then
+        while true; do
+            case "$TARGET" in
+                arm-unknown-linux-gnueabi);;
+                arm-unknown-linux-gnueabihf);;
+                armv7-unknown-linux-gnueabihf);;
+                i586-unknown-linux-gnu);;
+                i686-unknown-linux-gnu);;
+                powerpc-unknown-linux-gnu);;
+                armv5te-unknown-linux-gnueabi);;
+                mips-unknown-linux-gnu);;
+                mipsel-unknown-linux-gnu);;
+                powerpc-unknown-linux-gnuspe);;
+                riscv32gc-unknown-linux-gnu);;
+                sparc-unknown-linux-gnu);;
+                *) break;
+            esac
+            RUST_LIBC_TIME_BITS=32 test_target "$BUILD_CMD" "$TARGET" "$NO_STD"
+            RUST_LIBC_TIME_BITS=64 test_target "$BUILD_CMD" "$TARGET" "$NO_STD"
+            break # also build without RUST_LIBC_TIME_BITS set
+        done
+    fi
+
     # If there is a std component, fetch it:
     if [ "${NO_STD}" != "1" ]; then
         # FIXME: rustup often fails to download some artifacts due to network
diff --git a/ci/run-docker.sh b/ci/run-docker.sh
index 042303846f3fe..a00ca4321ffa3 100755
--- a/ci/run-docker.sh
+++ b/ci/run-docker.sh
@@ -43,6 +43,7 @@ run() {
       --env LIBC_CI_ZBUILD_STD \
       --env CARGO_HOME=/cargo \
       --env CARGO_TARGET_DIR=/checkout/target \
+      --env RUST_LIBC_TIME_BITS \
       --volume "$CARGO_HOME":/cargo \
       --volume "$(rustc --print sysroot)":/rust:ro \
       --volume "$(pwd)":/checkout:ro \