diff --git a/.github/workflows/QA.yaml b/.github/workflows/QA.yaml
index f0d3afb8..9269e548 100644
--- a/.github/workflows/QA.yaml
+++ b/.github/workflows/QA.yaml
@@ -40,3 +40,6 @@ jobs:
 
       - name: Check stubs annotations
         run: inv check-stub-annotations
+
+      - name: Check build deps are in sync
+        run: inv check-build-deps-sync
diff --git a/.github/workflows/Tests.yaml b/.github/workflows/Tests.yaml
index fef16bf8..a25cc3a6 100644
--- a/.github/workflows/Tests.yaml
+++ b/.github/workflows/Tests.yaml
@@ -73,6 +73,28 @@ jobs:
       - name: Run the tests
         run: inv coverage --args "-vvv"
 
+  build-floor-versions: # validate that the floor of our build deps ranges still works
+    runs-on: ubuntu-26.04
+
+    steps:
+      - uses: actions/checkout@v7
+
+      - name: Set up Python
+        uses: actions/setup-python@v7
+        with:
+          python-version: "3.11"
+
+      - name: Install floor versions of build dependencies
+        run: |
+          pip install -U pip packaging
+          pip install $(python3 scripts/floor_versions.py)
+
+      - name: Install project against floor versions (no build isolation)
+        run: pip install -e .[test,scripts] --no-build-isolation
+
+      - name: Run the tests
+        run: inv coverage --args "-vvv"
+
   build-docs: # validate that doc can be built
     runs-on: ubuntu-26.04
 
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8cf9de29..330fa057 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+
+- Relax `setuptools`/`wheel`/`cython` build dependency pins to `>=floor,<next major>` ranges instead of exact versions, easing downstream packaging; `delocate` stays exactly pinned (#288)
+
 ## [4.0.0] - 2026-10-29
 
 ### Added
diff --git a/pyproject.toml b/pyproject.toml
index a6b0256b..2c7413a6 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,8 +1,17 @@
 [build-system]
 requires = [
-  "setuptools == 84.2.1",
-  "wheel == 0.48.0",
-  "cython == 3.3.0",
+  # this list must stay byte-for-byte identical to [project.optional-dependencies].build
+  # below. PEP 518 requires build-system.requires to be static TOML, parsed before any
+  # project/build-backend code runs, so it cannot reference the `build` extra (or vice
+  # versa): the duplication is unavoidable and is checked by
+  # scripts/check_build_deps_sync.py (run in CI).
+  #
+  # floor versions below are read by scripts/floor_versions.py and
+  # validated by the "build-floor-versions" CI job; when bumping, only move
+  # the floor if actually required, not on every bump
+  "setuptools >=84.2.1,<85",
+  "wheel >=0.48.0,<0.49",
+  "cython >=3.3.0,<3.4",
   # https://github.com/pypa/cibuildwheel/blob/v2.22/cibuildwheel/resources/constraints.txt
   "delocate == 0.13.0 ; platform_system=='Windows'",
 ]
@@ -69,9 +78,11 @@ test = [
   "libzim[build]",
 ]
 build = [
-  "setuptools == 84.2.1",
-  "wheel == 0.48.0",
-  "cython == 3.3.0",
+  # must stay byte-for-byte identical to [build-system].requires above; see the
+  # comment there
+  "setuptools >=84.2.1,<85",
+  "wheel >=0.48.0,<0.49",
+  "cython >=3.3.0,<3.4",
   "delocate == 0.13.0 ; platform_system=='Windows'",
 ]
 docs = [
diff --git a/scripts/check_build_deps_sync.py b/scripts/check_build_deps_sync.py
new file mode 100644
index 00000000..9c1b694b
--- /dev/null
+++ b/scripts/check_build_deps_sync.py
@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+"""Check that build-system.requires and the `build` extra stay in sync.
+
+PEP 518 requires build-system.requires to be static TOML, parsed before any
+project or build-backend code runs, so it cannot reference
+project.optional-dependencies.build (or vice-versa): the two lists must be
+duplicated by hand. This script is the drift check for that duplication.
+"""
+
+import sys
+import tomllib
+from pathlib import Path
+
+
+def main() -> int:
+    pyproject = tomllib.loads(Path("pyproject.toml").read_text())
+    build_system_requires = pyproject["build-system"]["requires"]
+    build_extra = pyproject["project"]["optional-dependencies"]["build"]
+
+    if build_system_requires == build_extra:
+        print("build-system.requires and the `build` extra are in sync")  # noqa: T201
+        return 0
+
+    print(  # noqa: T201
+        "error: build-system.requires and the `build` extra have drifted apart"
+    )
+    print(f"  build-system.requires       = {build_system_requires}")  # noqa: T201
+    print(f"  optional-dependencies.build = {build_extra}")  # noqa: T201
+    return 1
+
+
+if __name__ == "__main__":
+    sys.exit(main())
diff --git a/scripts/floor_versions.py b/scripts/floor_versions.py
new file mode 100644
index 00000000..b47fa30f
--- /dev/null
+++ b/scripts/floor_versions.py
@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+"""Print `name==version` pins for the floor of build-system.requires in pyproject.toml.
+
+Used by CI to install and test against the lowest versions we claim to
+support, without hardcoding those versions a second time in the workflow.
+"""
+
+import tomllib
+from pathlib import Path
+
+from packaging.requirements import Requirement
+
+pyproject = tomllib.loads(Path("pyproject.toml").read_text())
+
+pins = []
+for req in pyproject["build-system"]["requires"]:
+    requirement = Requirement(req)
+    if requirement.marker and not requirement.marker.evaluate():
+        continue
+    # exact pins (e.g. delocate) have nothing to float, skip them
+    floor = next(
+        (spec.version for spec in requirement.specifier if spec.operator == ">="),
+        None,
+    )
+    if floor is not None:
+        pins.append(f"{requirement.name}=={floor}")
+
+print(" ".join(pins))  # noqa: T201
diff --git a/tasks.py b/tasks.py
index e0474fb0..4037dc6a 100644
--- a/tasks.py
+++ b/tasks.py
@@ -113,12 +113,19 @@ def check_stub_annotations(ctx: Context):
     ctx.run("python -m scripts.check_stub_annotations", pty=use_pty)
 
 
+@task
+def check_build_deps_sync(ctx: Context):
+    """check that build-system.requires and the build extra are in sync"""
+    ctx.run("python -m scripts.check_build_deps_sync", pty=use_pty)
+
+
 @task(optional=["args"], help={"args": "check tools (pyright) additional arguments"})
 def checkall(ctx: Context, args: str = ""):
     """check static types and type stubs"""
     check_pyright(ctx, args)
     check_stubtest(ctx)
     check_stub_annotations(ctx)
+    check_build_deps_sync(ctx)
 
 
 @task(optional=["args"], help={"args": "black additional arguments"})