diff --git a/LIBLCMS2_DYLIB_COLLISION.md b/LIBLCMS2_DYLIB_COLLISION.md
index e584a25a..ae139c91 100644
--- a/LIBLCMS2_DYLIB_COLLISION.md
+++ b/LIBLCMS2_DYLIB_COLLISION.md
@@ -243,9 +243,23 @@ Fixed and hardened on this branch:
   a future regression in this area is diagnosable from `negpy.log` alone
   instead of requiring a multi-day investigation like this one.
 
-Follow-up, not done here: generalize the symbol-closure check to every
-same-basename dylib collision in the bundle (not just liblcms2), which
-would also catch the pre-existing `libomp.dylib`/numba gap found while
-scoping this fix. `libjpeg`/`libpng`/`libz`/`libtiff` are vendored by
-multiple of the same packages and carry the same theoretical risk — no
-evidence any are currently broken, but untested.
+Follow-up, done: `check_bundled_dylib_collisions()` generalizes the
+symbol-closure check to every same-basename dylib collision under
+`Contents/Frameworks`, not just liblcms2. It scans the whole bundle rather
+than a curated list of risky basenames — a manual pass guessing which
+libraries might collide (by comparing vendored version strings across
+`cv2`/`PIL`/`rawpy`/`imagecodecs`) missed a real one: three packages vendor
+byte-different copies of `libjpeg.8.3.2.dylib`, invisible unless you check
+for repeated exact filenames rather than reasoning about version numbers.
+Also found real (currently benign — no missing symbols today) collisions on
+`libpng16.16.dylib` and `libtiff.6.dylib` (`cv2` vs `PIL`). Confirmed on the
+real local build: passes clean, and correctly raises when a canonical
+symlink is forced to point at a copy missing a symbol a sibling consumer
+needs.
+
+Still not done, deliberately: the `libomp.dylib`/numba gap. It's a
+different failure mode (PyInstaller not bundling the library at all, not a
+collision between multiple bundled copies), stays outside what this check
+looks for, and there is still no evidence it affects NegPy (numba's
+OpenMP-parallel pool is optional with a runtime fallback) — not worth
+fixing speculatively.
diff --git a/build.py b/build.py
index 43e8846d..cdb15bf8 100644
--- a/build.py
+++ b/build.py
@@ -1,3 +1,4 @@
+import functools
 import glob
 import os
 import platform
@@ -381,13 +382,81 @@ def fix_lcms2_dylib_collision():
         raise RuntimeError(f"imagecodecs' liblcms2.2.dylib is missing symbols other consumers need:\n{detail}")
 
 
-def _nm_symbols(path: str, *, defined: bool) -> set[str]:
+@functools.lru_cache(maxsize=None)
+def _nm_symbols(path: str, *, defined: bool) -> frozenset[str]:
     """Return a Mach-O file's defined-exported (-gU) or undefined (-u) symbol names."""
     flag = "-gU" if defined else "-u"
     out = subprocess.run(["nm", flag, path], capture_output=True, text=True, check=True).stdout
     if defined:
-        return {line.split()[-1] for line in out.splitlines() if line.strip()}
-    return {line.strip() for line in out.splitlines() if line.strip()}
+        return frozenset(line.split()[-1] for line in out.splitlines() if line.strip())
+    return frozenset(line.strip() for line in out.splitlines() if line.strip())
+
+
+@functools.lru_cache(maxsize=None)
+def _dylib_load_basenames(path: str) -> frozenset[str]:
+    """Basenames a Mach-O file references via LC_LOAD_DYLIB (its real, linked-in dependencies)."""
+    out = subprocess.run(["otool", "-L", path], capture_output=True, text=True, check=True).stdout
+    return frozenset(os.path.basename(line.split()[0]) for line in out.splitlines()[1:] if line.strip())
+
+
+def check_bundled_dylib_collisions():
+    """Verify every same-basename dylib PyInstaller collapsed to one canonical
+    copy still satisfies every real consumer's symbols.
+
+    Generalizes fix_lcms2_dylib_collision() to the whole bundle: cv2, PIL,
+    rawpy and imagecodecs each vendor their own copies of common libraries
+    (libjpeg, libpng, libtiff, ...) under identical filenames, and PyInstaller
+    keeps only one arbitrary pick as the canonical @rpath target for all of
+    them -- the exact bug class in LIBLCMS2_DYLIB_COLLISION.md, which this
+    scans for instead of relying on a curated list of known-risky basenames
+    (that fix's own consumer glob missed a real libjpeg collision on first
+    pass -- see the doc). Raises rather than warns, so a future dependency
+    bump that silently drops a symbol fails the build instead of shipping
+    broken silently.
+
+    Does not check libraries PyInstaller fails to bundle at all (e.g. numba's
+    optional libomp.dylib) -- that is a different failure mode (absence, not
+    a collision) with no evidence of user impact; see LIBLCMS2_DYLIB_COLLISION.md.
+    """
+    frameworks = os.path.join("dist", f"{APP_NAME}.app", "Contents", "Frameworks")
+    all_files = [
+        os.path.join(dirpath, name)
+        for dirpath, _, filenames in os.walk(frameworks)
+        for name in filenames
+        if name.endswith((".dylib", ".so"))
+    ]
+    by_basename: dict[str, list[str]] = {}
+    for path in all_files:
+        if not os.path.islink(path):
+            by_basename.setdefault(os.path.basename(path), []).append(path)
+
+    gaps = []
+    for basename, copies in by_basename.items():
+        canonical = os.path.join(frameworks, basename)
+        if not os.path.islink(canonical):
+            continue  # no top-level collapse for this basename -- nothing collided
+        canonical_real = os.path.realpath(canonical)
+        distinct = {p for p in copies if os.path.realpath(p) != canonical_real}
+        if not distinct:
+            continue  # every copy is byte-identical -- an arbitrary pick can't lose symbols
+        exports = _nm_symbols(canonical_real, defined=True)
+        provided_anywhere: set[str] = set(exports)
+        for p in distinct:
+            provided_anywhere |= _nm_symbols(p, defined=True)
+
+        for consumer in all_files:
+            if os.path.islink(consumer) or os.path.realpath(consumer) == canonical_real or consumer in distinct:
+                continue
+            if basename not in _dylib_load_basenames(consumer):
+                continue
+            needed = _nm_symbols(consumer, defined=False) & provided_anywhere
+            missing = needed - exports
+            if missing:
+                gaps.append((consumer, basename, sorted(missing)))
+
+    if gaps:
+        detail = "\n".join(f"  {os.path.relpath(c, frameworks)} needs {b}: missing {m}" for c, b, m in gaps)
+        raise RuntimeError(f"a bundled dylib collision leaves a consumer missing symbols:\n{detail}")
 
 
 def codesign_macos_app():
@@ -468,6 +537,7 @@ def build():
         package_windows()
     elif is_macos:
         fix_lcms2_dylib_collision()
+        check_bundled_dylib_collisions()
         codesign_macos_app()
         package_macos()