diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 00ef76f78..91f61810e 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -44,6 +44,8 @@ jobs:
         run: |
           rustup target add thumbv7m-none-eabi
           sudo apt-get -y install gcc-arm-none-eabi
+      - name: Check for unknown cfg tags
+        run: ci/check-cfg-flags.py
       - name: shellcheck the CI script
         if: "matrix.platform == 'ubuntu-latest'"
         run: |
diff --git a/ci/check-cfg-flags.py b/ci/check-cfg-flags.py
new file mode 100755
index 000000000..85cbde853
--- /dev/null
+++ b/ci/check-cfg-flags.py
@@ -0,0 +1,152 @@
+#!/usr/bin/env python3
+# Rust is fairly relaxed in checking the validity of arguments passed to #[cfg].
+# While it should probably be more strict when checking features, it cannot be
+# strict when checking loose cfg tags, because those can be anything and are
+# simply passed to rustc via unconstrained arguments.
+#
+# Thus, we do it for rustc manually, but scanning all our source and checking
+# that all our cfg tags match a known cfg tag.
+import sys, glob, re
+
+def check_feature(feature):
+    if feature == "std":
+        pass
+    elif feature == "no-std":
+        pass
+    elif feature == "hashbrown":
+        pass
+    elif feature == "backtrace":
+        pass
+    elif feature == "grind_signatures":
+        pass
+    elif feature == "unsafe_revoked_tx_signing":
+        pass
+    elif feature == "futures":
+        pass
+    elif feature == "tokio":
+        pass
+    elif feature == "rest-client":
+        pass
+    elif feature == "rpc-client":
+        pass
+    elif feature == "serde":
+        pass
+    elif feature == "esplora-blocking":
+        pass
+    elif feature == "esplora-async":
+        pass
+    elif feature == "async-interface":
+        pass
+    elif feature == "electrum":
+        pass
+    elif feature == "_test_utils":
+        pass
+    elif feature == "_test_vectors":
+        pass
+    elif feature == "afl":
+        pass
+    elif feature == "honggfuzz":
+        pass
+    elif feature == "libfuzzer_fuzz":
+        pass
+    elif feature == "stdin_fuzz":
+        pass
+    elif feature == "max_level_off":
+        pass
+    elif feature == "max_level_error":
+        pass
+    elif feature == "max_level_warn":
+        pass
+    elif feature == "max_level_info":
+        pass
+    elif feature == "max_level_debug":
+        pass
+    elif feature == "max_level_trace":
+        pass
+    else:
+        print("Bad feature: " + feature)
+        assert False
+
+def check_target_os(os):
+    if os == "windows":
+        pass
+    else:
+        assert False
+
+def check_cfg_tag(cfg):
+    if cfg == "fuzzing":
+        pass
+    elif cfg == "test":
+        pass
+    elif cfg == "debug_assertions":
+        pass
+    elif cfg == "c_bindings":
+        pass
+    elif cfg == "ldk_bench":
+        pass
+    elif cfg == "taproot":
+        pass
+    elif cfg == "require_route_graph_test":
+        pass
+    else:
+        print("Bad cfg tag: " + cfg)
+        assert False
+
+def check_cfg_args(cfg):
+    if cfg.startswith("all(") or cfg.startswith("any(") or cfg.startswith("not("):
+        brackets = 1
+        pos = 4
+        while pos < len(cfg):
+            if cfg[pos] == "(":
+                brackets += 1
+            elif cfg[pos] == ")":
+                brackets -= 1
+                if brackets == 0:
+                    check_cfg_args(cfg[4:pos])
+                    if pos + 1 != len(cfg):
+                        assert cfg[pos + 1] == ","
+                        check_cfg_args(cfg[pos + 2:].strip())
+                    return
+            pos += 1
+        assert False
+        assert(cfg.endswith(")"))
+        check_cfg_args(cfg[4:len(cfg)-1])
+    else:
+        parts = [part.strip() for part in cfg.split(",", 1)]
+        if len(parts) > 1:
+            for part in parts:
+                check_cfg_args(part)
+        elif cfg.startswith("feature") or cfg.startswith("target_os") or cfg.startswith("target_pointer_width"):
+            arg = cfg
+            if cfg.startswith("feature"):
+                arg = arg[7:].strip()
+            elif cfg.startswith("target_os"):
+                arg = arg[9:].strip()
+            else:
+                arg = arg[20:].strip()
+            assert arg.startswith("=")
+            arg = arg[1:].strip()
+            assert arg.startswith("\"")
+            assert arg.endswith("\"")
+            arg = arg[1:len(arg)-1]
+            assert not "\"" in arg
+            if cfg.startswith("feature"):
+                check_feature(arg)
+            elif cfg.startswith("target_os"):
+                check_target_os(arg)
+            else:
+                assert arg == "32" or arg == "64"
+        else:
+            check_cfg_tag(cfg.strip())
+
+cfg_regex = re.compile("#\[cfg\((.*)\)\]")
+for path in glob.glob(sys.path[0] + "/../**/*.rs", recursive = True):
+    with open(path, "r") as file:
+        while True:
+            line = file.readline()
+            if not line:
+                break
+            if "#[cfg(" in line:
+                if not line.strip().startswith("//"):
+                    cfg_part = cfg_regex.match(line.strip()).group(1)
+                    check_cfg_args(cfg_part)