diff --git a/build.rs b/build.rs
index b9a8305918518..87a55e6c98d14 100644
--- a/build.rs
+++ b/build.rs
@@ -35,6 +35,9 @@ const ALLOWED_CFGS: &[&str] = &[
     // Corresponds to `_REDIR_TIME64` in musl: symbol redirects to __*_time64
     "musl_redir_time64",
     "vxworks_lt_25_09",
+    // Exists for Windows x86 GNU to use a 64-bit wide `time_t` instead of the
+    // incorrect 32-bit wide `time_t` that we have on stable.
+    "windows_gnu_time64",
 ];
 
 // Extra values to allow for check-cfg.
@@ -131,6 +134,14 @@ fn main() {
         }
     }
 
+    if target_arch == "x86"
+        && target_os == "windows"
+        && target_env == "gnu"
+        && env_flag("CARGO_CFG_LIBC_UNSTABLE_WINDOWS_GNU_TIME64")
+    {
+        set_cfg("windows_gnu_time64");
+    }
+
     let linux_time_bits64 = env::var("RUST_LIBC_UNSTABLE_LINUX_TIME_BITS64").is_ok();
     println!("cargo:rerun-if-env-changed=RUST_LIBC_UNSTABLE_LINUX_TIME_BITS64");
     if linux_time_bits64 {
diff --git a/ci/run.sh b/ci/run.sh
index 96e5750945df4..2a0ed5b8b533c 100755
--- a/ci/run.sh
+++ b/ci/run.sh
@@ -54,4 +54,5 @@ if [ "$env" = "gnu" ] && [ "$bits" = "32" ]; then
     RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS=64 $cmd -- $test_flags
     # shellcheck disable=SC2086
     RUST_LIBC_UNSTABLE_GNU_TIME_BITS=64 $cmd -- $test_flags
+    RUSTFLAGS="$RUSTFLAGS --cfg=libc_unstable_windows_gnu_time64=\"1\"" $cmd -- $test_flags
 fi
diff --git a/ci/verify-build.py b/ci/verify-build.py
index 831c1cdb3d3ec..817ecc8a26933 100755
--- a/ci/verify-build.py
+++ b/ci/verify-build.py
@@ -242,8 +242,12 @@ def run(
     args: Sequence[str | Path],
     *,
     env: Optional[dict[str, str]] = None,
+    extra_rustflags: Optional[str] = None,
     check: bool = True,
 ) -> sp.CompletedProcess:
+    if extra_rustflags is not None:
+        env["RUSTFLAGS"] = env.get("RUSTFLAGS", "") + " " + extra_rustflags
+
     xtrace(args, env=env)
     return sp.run(args, env=env, check=check)
 
@@ -396,6 +400,9 @@ def test_target(cfg: Cfg, target: Target) -> TargetResult:
         run(cmd, env=env | {"RUST_LIBC_UNSTABLE_GNU_FILE_OFFSET_BITS": "64"})
         # Equivalent of _TIME_BITS=64
         run(cmd, env=env | {"RUST_LIBC_UNSTABLE_GNU_TIME_BITS": "64"})
+        # For Windows x86 GNU to test out a backwards-incompatible 64-bit wide
+        # `time_t`
+        run(cmd, env=env, extra_rustflags="--cfg=libc_unstable_windows_gnu_time64=\"1\"")
 
     if "musl" in target_env:
         # Check with breaking changes from musl, including 64-bit time_t on 32-bit
diff --git a/src/windows/mod.rs b/src/windows/mod.rs
index 2cfd1977d2799..866ed90d62629 100644
--- a/src/windows/mod.rs
+++ b/src/windows/mod.rs
@@ -19,7 +19,7 @@ pub type clock_t = i32;
 pub type errno_t = c_int;
 
 cfg_if! {
-    if #[cfg(all(target_arch = "x86", target_env = "gnu"))] {
+    if #[cfg(all(target_arch = "x86", target_env = "gnu", not(windows_gnu_time64)))] {
         pub type time_t = i32;
     } else {
         pub type time_t = i64;
@@ -34,6 +34,12 @@ extern_ty! {
     pub enum timezone {}
 }
 
+#[deprecated(
+    since = "1.0.0",
+    note = "This time-related value, among others, is part of the shift \
+            towards using a single, 64-bit-sized `time_t`. See #PENDING for \
+            discussion."
+)]
 pub type time64_t = i64;
 
 pub type SOCKET = crate::uintptr_t;