diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index b32c9f47f4..708b6e50f4 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -149,6 +149,30 @@ jobs:
           RUST_VERSION: stable
           WASM: wasm_emscripten
 
+  wasm_unknown:
+    strategy:
+      matrix:
+        os: [ubuntu-latest]
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install rust
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+          target: wasm32-unknown-unknown
+          override: true
+          default: true
+
+      - name: Build and Test
+        run: bash ci/github.sh
+        env:
+          RUST_VERSION: stable
+          WASM: wasm_unknown
+
   cross-targets:
     strategy:
       matrix:
diff --git a/ci/github.sh b/ci/github.sh
index 081a128b90..6512f9a7ee 100755
--- a/ci/github.sh
+++ b/ci/github.sh
@@ -36,6 +36,8 @@ meaningful in the github actions feature matrix UI.
             test_wasm_simple
         elif [[ ${WASM:-} == wasm_emscripten ]]; then
             test_wasm_emscripten
+        elif [[ ${WASM:-} == wasm_unknown ]]; then
+            test_wasm_unknown
         elif [[ ${CORE:-} == no_std ]]; then
             test_core
         elif [[ ${EXHAUSTIVE_TZ:-} == all_tzs ]]; then
@@ -118,4 +120,8 @@ test_wasm_emscripten() {
     runt cargo build --target wasm32-unknown-emscripten
 }
 
+test_wasm_unknown() {
+    runt cargo build --target wasm32-unknown-unknown
+}
+
 main "$@"
diff --git a/src/offset/sys/stub.rs b/src/offset/sys/stub.rs
new file mode 100644
index 0000000000..616b52fe5e
--- /dev/null
+++ b/src/offset/sys/stub.rs
@@ -0,0 +1,80 @@
+// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use super::Tm;
+
+fn time_to_tm(ts: i64, tm: &mut Tm) {
+    let leapyear = |year| -> bool { year % 4 == 0 && (year % 100 != 0 || year % 400 == 0) };
+
+    static YTAB: [[i64; 12]; 2] = [
+        [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
+        [31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31],
+    ];
+
+    let mut year = 1970;
+
+    let dayclock = ts % 86400;
+    let mut dayno = ts / 86400;
+
+    tm.tm_sec = (dayclock % 60) as i32;
+    tm.tm_min = ((dayclock % 3600) / 60) as i32;
+    tm.tm_hour = (dayclock / 3600) as i32;
+    tm.tm_wday = ((dayno + 4) % 7) as i32;
+    loop {
+        let yearsize = if leapyear(year) { 366 } else { 365 };
+        if dayno >= yearsize {
+            dayno -= yearsize;
+            year += 1;
+        } else {
+            break;
+        }
+    }
+    tm.tm_year = (year - 1900) as i32;
+    tm.tm_yday = dayno as i32;
+    let mut mon = 0;
+    while dayno >= YTAB[if leapyear(year) { 1 } else { 0 }][mon] {
+        dayno -= YTAB[if leapyear(year) { 1 } else { 0 }][mon];
+        mon += 1;
+    }
+    tm.tm_mon = mon as i32;
+    tm.tm_mday = dayno as i32 + 1;
+    tm.tm_isdst = 0;
+}
+
+fn tm_to_time(tm: &Tm) -> i64 {
+    let mut y = tm.tm_year as i64 + 1900;
+    let mut m = tm.tm_mon as i64 + 1;
+    if m <= 2 {
+        y -= 1;
+        m += 12;
+    }
+    let d = tm.tm_mday as i64;
+    let h = tm.tm_hour as i64;
+    let mi = tm.tm_min as i64;
+    let s = tm.tm_sec as i64;
+    (365 * y + y / 4 - y / 100 + y / 400 + 3 * (m + 1) / 5 + 30 * m + d - 719561) * 86400
+        + 3600 * h
+        + 60 * mi
+        + s
+}
+
+pub(super) fn time_to_local_tm(sec: i64, tm: &mut Tm) {
+    // FIXME: Add timezone logic
+    time_to_tm(sec, tm);
+}
+
+pub(super) fn utc_tm_to_time(tm: &Tm) -> i64 {
+    tm_to_time(tm)
+}
+
+pub(super) fn local_tm_to_time(tm: &Tm) -> i64 {
+    // FIXME: Add timezone logic
+    tm_to_time(tm)
+}