diff --git a/pio-scripts/validate_usermods.py b/pio-scripts/validate_usermods.py
new file mode 100644
index 000000000..50d51f99f
--- /dev/null
+++ b/pio-scripts/validate_usermods.py
@@ -0,0 +1,92 @@
+import re
+import sys
+from pathlib import Path   # For OS-agnostic path manipulation
+from click import secho
+from SCons.Script import Action, Exit
+from platformio import util
+
+def read_lines(p: Path):
+    """ Read in the contents of a file for analysis """
+    with p.open("r", encoding="utf-8", errors="ignore") as f:
+        return f.readlines()
+
+def check_map_file_objects(map_file: list[str], usermod_dirs: list[str]) -> set[str]:
+    """ Checks that an object file from each usermod_dir appears in the linked output
+
+        Returns the (sub)set of usermod_dirs that are found in the output ELF
+    """
+    # Pattern to match symbols in object directories
+    # Join directories into alternation
+    usermod_dir_regex = "|".join([re.escape(dir) for dir in usermod_dirs])
+    # Matches nonzero address, any size, and any path in a matching directory
+    object_path_regex = re.compile(r"0x0*[1-9a-f][0-9a-f]*\s+0x[0-9a-f]+\s+\S+/(" + usermod_dir_regex + r")/\S+\.o")
+
+    found = set()
+    for line in map_file:
+        matches = object_path_regex.findall(line)
+        for m in matches:
+            found.add(m)
+    return found
+
+def count_registered_usermods(map_file: list[str]) -> int:
+    """ Returns the number of usermod objects in the usermod list """
+    # Count the number of entries in the usermods table section
+    return len([x for x in map_file if ".dtors.tbl.usermods.1" in x])
+
+
+def validate_map_file(source, target, env):
+    """ Validate that all usermods appear in the output build """
+    build_dir = Path(env.subst("$BUILD_DIR"))
+    map_file_path = build_dir /  env.subst("${PROGNAME}.map")
+
+    if not map_file_path.exists():
+        secho(f"ERROR: Map file not found: {map_file_path}", fg="red", err=True)
+        Exit(1)
+
+    # Load project settings
+    usermods = env.GetProjectOption("custom_usermods","").split()
+    libdeps = env.GetProjectOption("lib_deps", [])
+    lib_builders = env.GetLibBuilders()
+
+    secho(f"INFO: Expecting {len(usermods)} usermods: {', '.join(usermods)}")
+
+    # Map the usermods to libdeps; every usermod should have one
+    usermod_dirs = []
+    for mod in usermods:
+        modstr = f"{mod} = symlink://"
+        this_mod_libdeps = [libdep[len(modstr):] for libdep in libdeps if libdep.startswith(modstr)]
+        if not this_mod_libdeps:
+            secho(
+                f"ERROR: Usermod {mod} not found in build libdeps!",
+                fg="red",
+                err=True)
+            Exit(1)
+        # Save only the final folder name
+        usermod_dir = Path(this_mod_libdeps[0]).name
+        # Search lib_builders
+        this_mod_builders = [builder for builder in lib_builders if Path(builder.src_dir).name == usermod_dir]
+        if not this_mod_builders:
+            secho(
+                f"ERROR: Usermod {mod} not found in library builders!",
+                fg="red",
+                err=True)
+            Exit(1)
+        usermod_dirs.append(usermod_dir)
+
+    # Now parse the map file
+    map_file_contents = read_lines(map_file_path)
+    confirmed_usermods = check_map_file_objects(map_file_contents, usermod_dirs)
+    usermod_object_count = count_registered_usermods(map_file_contents)
+
+    secho(f"INFO: {len(usermod_dirs)}/{len(usermods)} libraries linked via custom_usermods, producing {usermod_object_count} usermod object entries")
+    missing_usermods = confirmed_usermods.difference(usermod_dirs)
+    if missing_usermods:
+        secho(
+            f"ERROR: No object files from {missing_usermods} found in linked output!",
+            fg="red",
+            err=True)
+        Exit(1)
+    return None
+
+Import("env")
+env.AddPostAction("$BUILD_DIR/${PROGNAME}.elf", Action(validate_map_file, cmdstr='Checking map file...'))
diff --git a/platformio.ini b/platformio.ini
index a7485244c..b713a2d39 100644
--- a/platformio.ini
+++ b/platformio.ini
@@ -116,6 +116,7 @@ extra_scripts =
   pre:pio-scripts/user_config_copy.py
   pre:pio-scripts/load_usermods.py
   pre:pio-scripts/build_ui.py
+  post:pio-scripts/validate_usermods.py  ;; double-check the build output usermods
   ; post:pio-scripts/obj-dump.py  ;; convenience script to create a disassembly dump of the firmware (hardcore debugging)
 
 # ------------------------------------------------------------------------------