diff --git a/examples/generated/source_sync/example.pdf b/examples/generated/source_sync/example.pdf
index b05c770..917cb44 100644
Binary files a/examples/generated/source_sync/example.pdf and b/examples/generated/source_sync/example.pdf differ
diff --git a/typst/private/tests/simple/BUILD.bazel b/typst/private/tests/simple/BUILD.bazel
index 46c1483..04f62a3 100644
--- a/typst/private/tests/simple/BUILD.bazel
+++ b/typst/private/tests/simple/BUILD.bazel
@@ -1,5 +1,6 @@
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
 load("@bazel_skylib//rules:copy_file.bzl", "copy_file")
+load("@bazel_skylib//rules:diff_test.bzl", "diff_test")
 load("//typst:typst.bzl", "typst")
 
 filegroup(
@@ -29,3 +30,29 @@ build_test(
         ":simple",
     ],
 )
+
+# Determinism test: two separate targets from the same source must produce
+# byte-identical PDFs (SOURCE_DATE_EPOCH=0 is set by default).
+typst(
+    name = "deterministic_a",
+    src = "simple.typ",
+    data = [
+        ":frown",
+        ":smile",
+    ],
+)
+
+typst(
+    name = "deterministic_b",
+    src = "simple.typ",
+    data = [
+        ":frown",
+        ":smile",
+    ],
+)
+
+diff_test(
+    name = "deterministic_test",
+    file1 = ":deterministic_a",
+    file2 = ":deterministic_b",
+)
diff --git a/typst/private/typst.bzl b/typst/private/typst.bzl
index 6627ba2..7894ea9 100644
--- a/typst/private/typst.bzl
+++ b/typst/private/typst.bzl
@@ -33,6 +33,9 @@ def _typst_impl(ctx):
             _rlocationpath(src, ctx.workspace_name),
         ))
 
+    env = {"SOURCE_DATE_EPOCH": "0"}
+    env.update(ctx.attr.env)
+
     ctx.actions.run(
         mnemonic = "TypstC",
         executable = toolchain_info.process_wrapper,
@@ -40,6 +43,7 @@ def _typst_impl(ctx):
         outputs = [pdf_outfile],
         tools = toolchain_info.all_files,
         inputs = depset([ctx.file.src] + ctx.files.data),
+        env = env,
     )
 
     return [
@@ -48,16 +52,21 @@ def _typst_impl(ctx):
     ]
 
 typst = rule(
-    doc = "TODO",
+    doc = "Compile a Typst document to PDF.",
     implementation = _typst_impl,
     attrs = {
         "data": attr.label_list(
-            doc = "TODO",
+            doc = "Additional data dependencies (images, templates, etc.).",
             allow_files = True,
             mandatory = False,
         ),
+        "env": attr.string_dict(
+            doc = "Additional environment variables for the typst compiler action. " +
+                  "SOURCE_DATE_EPOCH=0 is set by default for deterministic output. " +
+                  "Override with a different value to opt out.",
+        ),
         "src": attr.label(
-            doc = "TODO",
+            doc = "The .typ source file to compile.",
             allow_single_file = [".typ"],
             mandatory = True,
         ),